dsPIC33FJ128GP206,MCP3909 Ref Design Guide Datasheet by Microchip Technology

Q MICROCHIP

MCP3909 / dsPIC33FJ128GP206

3-Phase Energy Meter

Reference Design

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6‘ MICROCHIP

MCP3909 / dsPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Table of Contents

Preface ........................................................................................................................... 7

Introduction............................................................................................................ 7

Document Layout .................................................................................................. 8

Conventions Used in this Guide............................................................................ 9

Recommended Reading...................................................................................... 10

The Microchip Web Site ...................................................................................... 10

Customer Support ............................................................................................... 10

Document Revision History................................................................................. 10

Chapter 1. Meter Overview

1.1 Introduction ................................................................................................... 11

1.2 Meter Design Parameters ............................................................................ 11

1.3 Power Calculations ....................................................................................... 12

1.4 Getting Started ............................................................................................. 13

Chapter 2. Hardware Description

2.1 Overview ...................................................................................................... 17

2.2 Analog Front End Circuitry ........................................................................... 18

2.3 Analog-To-Digital Conversion ...................................................................... 20

2.4 dspic33f Hardware Connection And Peripheral Usage ................................ 22

2.5 Power Supply ............................................................................................... 25

Chapter 3. Firmware

3.1 Overview ...................................................................................................... 27

3.2 Main Loop ..................................................................................................... 27

3.3 Calculation() - Calculating Electrical Parameters ......................................... 29

3.4 ADC Sampling Scheme For Calculations .................................................... 33

3.5 ReadING A/D Data Of The MCP3909 Device .............................................. 35

3.6 Communication Of UART Interface .............................................................. 37

3.7 Resource Configuration ................................................................................ 37

3.8 Description Of Project Files .......................................................................... 38

Chapter 4. Meter Calibration

4.1 Introduction ................................................................................................... 39

4.2 Current/voltage Calibration .......................................................................... 39

4.3 Apparent Power Calibration ......................................................................... 40

4.4 Phase Lag Calibration ................................................................................. 41

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

Chapter 5. PC Software

5.1 Overview And Installation ............................................................................. 43

5.2 Establish Communication ............................................................................. 44

5.3 Basic Parameters Output Screen ................................................................. 45

5.4 Phase A/B/C Harmonic Output Screen ........................................................ 45

5.5 Distortion Rate .............................................................................................. 46

5.6 Harmonic Power ........................................................................................... 46

5.7 Energy Accumulation ................................................................................... 47

5.8 Calibration Step 1 - Reset All Calibration ..................................................... 47

5.9 Linearity Calibration ...................................................................................... 48

5.10 Apparent Power Calibration ....................................................................... 49

5.11 Phase Lag Calibration ................................................................................ 50

Chapter 6. Meter Communications Protocol

6.1 Introduction ................................................................................................... 51

6.2 Test Connection Command .......................................................................... 52

6.3 Total Data Request ...................................................................................... 52

6.4 Status Register ............................................................................................. 54

6.5 Harmonic Content Command ....................................................................... 54

6.6 Total Harmonic Distortion (THD) Command ................................................ 55

6.7 Start Energy Measurement Command ......................................................... 56

6.8 Stop Energy Measurement Command ......................................................... 56

6.9 Harmonic Power Command ......................................................................... 57

6.10 Calibrate Meter Voltage/current Command ................................................ 58

6.11 Calibrate Phase Lag Command ................................................................. 59

6.12 Calibrate Apparent Power Command ......................................................... 59

6.13 Calibrate Energy Pulse Command ............................................................. 60

6.14 Reset All Meter Calibration Values Command ........................................... 60

6.15 Calibrate Meter Constant (Energy Pulse Output Constant) ....................... 61

Appendix A. Schematics and Layouts

A.1 Introduction .................................................................................................. 63

A.2 Schematics And Pcb Layout ........................................................................ 63

Appendix B. Bill Of Materials (BOM)

Appendix C. Power Calculation Theory

C.1 Overview ...................................................................................................... 75

C.2 Synchronous Sampling And Quasi-synchronous Sampling ........................ 75

C.3 The Harmonic Analysis Algorithm Of Quasi-synchronous Sampling ........... 82

C.4 Measuring The Voltage/current Rms Value And Power Using Quasi-synchro-

nous Sampling Algorithm ........................................................................ 84

C.5 Measuring Frequency .................................................................................. 87

C.6 Improving Measurement Precision Of Quasi-synchronous Sampling Algorithm

................................................................................................................. 89

C.7 Measuring Secondary Parameters .............................................................. 91

C.8 Apparent Power Of Each Phase And Total Apparent Power ....................... 91

C.9 Power Factor Of Each Phase And Total Power Factor ............................... 91

C.10 Active Energy And Reactive Energy .......................................................... 92

C.11 Positive/negative Active Energy, Positive/negative Reactive Energy And

Four-quadrant Reactive Energy ............................................................. 92

C.12 Harmonic Components Of Current, Voltage And Total Harmonic Distortion

................................................................................................................. 94

C.13 Compensation For Ratio Error And Phase Lag ......................................... 95

C.14 Relationship Between Error And Current ................................................... 96

C.15 Ratio Error Compensation ......................................................................... 97

C.16 Phase Lag Compensation ......................................................................... 98

Appendix D. 50/60 Hz Meter Operation

D.1 Firmware Versions ..................................................................................... 103

Worldwide Sales and Service .................................................................................. 104

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

NOTES:

6‘ MICROCHIP

MCP3909 / dsPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Preface

INTRODUCTION

This chapter contains general information that will be useful to know before using the

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design. Items discussed in

this chapter include:

• Document Layout

• Conventions Used in this Guide

• Recommended Reading

• The Microchip Web Site

• Customer Support

• Document Revision History

NOTICE TO CUSTOMERS

All documentation becomes dated, and this manual is no exception. Microchip tools and

documentation are constantly evolving to meet customer needs, so some actual dialogs

and/or tool descriptions may differ from those in this document. Please refer to our web site

(www.microchip.com) to obtain the latest documentation available.

Documents are identified with a “DS” number. This number is located on the bottom of each

page, in front of the page number. The numbering convention for the DS number is

“DSXXXXXA”, where “XXXXX” is the document number and “A” is the revision level of the

document.

For the most up-to-date information on development tools, see the MPLAB® IDE on-line help.

Select the Help menu, and then Topics to open a list of available on-line help files.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

DOCUMENT LAYOUT

This document describes how to use the MCP3909 / dsPIC33F 3-Phase Energy Meter

Reference Design as a development tool to emulate and debug firmware on a target

board. The manual layout is as follows:

This document describes how to use the MCP3909 / dsPIC33F 3-Phase Energy Meter

Reference Design as a development tool. The manual layout is as follows:

•Chapter 1. “Meter Overview” - Summarizes the meter specifications and a quick

getting started section

•Chapter 2. “Hardware Description” - A detailed explanation of the different

circuit blocks, their function, and implementation

•Chapter 3. “Firmware” - All the calculations performed by the dsPIC33F are

described here

•Chapter 4. “Meter Calibration” - Explains how the meter is calibrated to

accuracy

•Chapter 5. “PC Software” - Includes screen shots of the viewer/calibration

software included with the system

•Chapter 6. “Meter Communications Protocol” - The UART commands used to

communicate to the meter

•Appendix A. “Schematics and Layouts” - Both PCB, SCH files are located here

for the 2 board system

•Appendix B. “Bill Of Materials (BOM)” - Part number and ordering information

for all components of the energy meter

•Appendix C. “Power Calculation Theory” - A detailed explanation of the theory

behind the calculations described in Chapter 3. “Firmware”

•Appendix D. “50/60 Hz Meter Operation” - Instructions on converting the meter

for use in a 60 Hz line frequency environment

MPLABW Hle>Sa vs

Preface

CONVENTIONS USED IN THIS GUIDE

This manual uses the following documentation conventions:

DOCUMENTATION CONVENTIONS

Description Represents Examples

Arial font:

Italic characters Referenced books MPLAB® IDE User’s Guide

Emphasized text ...is the only compiler...

Initial caps A window the Output window

A dialog the Settings dialog

A menu selection select Enable Programmer

Quotes A field name in a window or

dialog “Save project before build”

Underlined, italic text with

right angle bracket A menu path File>Save

Bold characters A dialog button Click OK

A tab Click the Power tab

N‘Rnnnn A number in verilog format,

where N is the total number of

digits, R is the radix and n is a

digit.

4‘b0010, 2‘hF1

Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>

Courier New font:

Plain Courier New Sample source code #define START

Filenames autoexec.bat

File paths c:\mcc18\h

Keywords _asm, _endasm, static

Command-line options -Opa+, -Opa-

Bit values 0, 1

Constants 0xFF, ‘A’

Italic Courier New A variable argument file.o, where file can be

any valid filename

Square brackets [ ] Optional arguments mcc18 [options] file

[options]

Curly brackets and pipe

character: { | } Choice of mutually exclusive

arguments; an OR selection errorlevel {0|1}

Ellipses... Replaces repeated text var_name [,

var_name...]

Represents code supplied by

user void main (void)

{ ...

}

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

RECOMMENDED READING

This user's guide describes how to use MCP3909 / dsPIC33F 3-Phase Energy Meter

Reference Design. Other useful documents are listed below. The following Microchip

documents are available and recommended as supplemental reference resources.

MCP3909 Data Sheet, “Energy Metering IC with SPI Interface and Active Power

Pulse Output“ (DS22025)

This data sheet provides detailed information regarding the MCP3909 device.

AN994 Application Note “IEC61036 Meter Design using the MCP3905/6 Energy

Metering Devices” (DS00994)

This application note documents the design decisions associated with using the

MCP390X devices for energy meter design and IEC compliance.

THE MICROCHIP WEB SITE

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site is used as a means to make files and information easily available to customers.

Accessible by using your favorite Internet browser, the web site contains the following

information:

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programs, design resources, user’s guides and hardware support documents,

latest software releases and archived software

•General Technical Support – Frequently Asked Questions (FAQs), technical

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member listing

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distributors and factory representatives

CUSTOMER SUPPORT

Users of Microchip products can receive assistance through several channels:

• Distributor or Representative

• Local Sales Office

• Field Application Engineer (FAE)

• Technical Support

Customers should contact their distributor, representative or field application engineer

(FAE) for support. Local sales offices are also available to help customers. A listing of

sales offices and locations is included in the back of this document.

Technical support is available through the web site at: http://support.microchip.com

DOCUMENT REVISION HISTORY

Revision A (November 2009)

• Initial Release of this Document.

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 1. Meter Overview

1.1 INTRODUCTION

The MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design is a fully

functional energy meter with many advanced features such as harmonic analysis, per

phase distortion information, voltage sag detection, four quadrant energy measure-

ment, and active and reactive power calculation. It uses Microchip’s powerful 16-bit

dsPIC33F Microcontroller Unit (MCU).

The MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design is unique in the

fact that all calculations take advantage of the dsPIC33F DSP engine, and all output

quantities are calculated in the frequency domain through the use of direct fourier

transforms (DFT). This approach yields a large volume of outputs for a variety of meter

designs, from simple active power only energy meters, to advanced energy meters

requiring harmonic analysis.

Another significant advantage of this design, is that the dsPIC firmware implements a

quasi-synchronous sampling algorithm, eliminating the need for external zero-crossing

detection and PLL (Phase Locked Loop) circuit for the synchronization of ADC samples

to line frequency. The line frequency is measured in software and corrected for mea-

surement errors caused by frequency fluctuations in the power grid. This additional

processing on the dsPIC reduces the overall meter cost by eliminating the requirement

for a PLL circuit.

1.2 METER DESIGN PARAMETERS

• Accuracy Class: 0.2S

• Rated Current Ib: 3 X 5(20)A

• 3-phase 4-wire System

• Line Frequency Range: 47-53 Hz or 57-63 Hz

(firmware option, see Appendix D. “50/60 Hz Meter Operation”)

• ADC Sampling Rate: 12.8 ksps to 3.2 ksps

• Voltage Input:

- 3 x 220/380V

- 3 x 57.7/100V (3-Phase, 4-Wire)

• Starting Current: 0.001 IB

• Active Power Measurement Range: 0-13200W, Precision Class: 0.2.

• Reactive Power Measurement Range: 0-13200VAR, Precision Class: 0.2.

• Power Factor (PF) Precision Class: 0.2.

• Frequency Measurement: Precision Class: 0.2, Max. Error 0.1 Hz

• Harmonic Component Measurement of Voltage Input: 2ND-31ST Harmonic

• Harmonic Component Measurement of Current Input: 2ND-31ST Harmonic

• Creeping: Anti-creeping Design (<0.0008 IB)

• Two Pulse Outputs: Total Phase Active Power, Total Phase Reactive Power

• Pulse Constant: 3200 Imp/kWh

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

1.3 POWER CALCULATIONS

A summary of all the calculations performed by this energy meter are summarized

below.

Chapter 3. “Firmware” provides an explanation on the firmware implementation,

Appendix C. “Power Calculation Theory” is included to show the theory behind this

firmware.

• Power Grid Frequency

• RMS Voltage Of Each Phase

• RMS Current Of Each Phase

• RMS Neutral Current

• Active Power Of Each Phase

• Reactive Power Of Each Phase

• Apparent Power Of Each Phase

• Power Factor Of Each Phase

• Fundamental Active Power Of Each Phase

• Fundamental Reactive Power Of Each Phase

• Harmonic Active Power Of Each Phase

• Harmonic Reactive Power Of Each Phase

• Total Active Power:

- The Algebraic Sum Of Active Power Of Three Phases

• Total Reactive Power:

- The Algebraic Sum Of Reactive Power Of Three Phases

• Total Apparent Power:

- The Algebraic Sum Of Apparent Power Of Three Phases

• Total Power Factor

• Phase Missing / Line voltage sag detection and alarm

• Total Active Energy:

- The Algebraic Sum Of Positive/negative Active Energy

• Positive/negative Active Energy

• Positive/negative Reactive Energy

• Four-quadrant Reactive Energy

• Voltage/current Harmonic Content Of Each Phase

Meter Overview

FIGURE 1-1: MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design.

1.4 GETTING STARTED

To describe how to use the MCP3909 / dsPIC33F 3-Phase Energy Meter Reference

Design, the following example is given using a 4-wire, 3-phase, 220VAC line voltage

and connection. The rated current of the energy meter is 5(20)A.

The energy meters are not shipped fully calibrated, and a full calibration should be

performed to show the true meter accuracy. See Chapter 4. “Meter Calibration” for

more information.

All connections described in this section are dependent on the choice of current

sensing element and a secondary external transformer may be required in higher

current meter designs.

dsPIC33 MCP3909

ICD Interface

UART Interface Current Transformer

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

Step 1: Connect the meter to 220V line and load

The diagram below shows where the voltage and current connections should be made.

It is not required to connect all 3 phases for the meter to be operational.

220VAC should be placed between either VA, VB, VC and NIN, NOUT.

The AC load for a given phase should then be connected to the IIN and IOUT of a given

phase.

FIGURE 1-2: Meter Case Bottom.

Step 2: Turn On Line/Load Power to the Meter

Turn on the power to the energy meter. D1 should be lit showing the meter has power.

At this point, if a load is connected and the meter is measuring power, the power LED,

D1, should be blinking.

IAIN IAOUT

VA IBIN IBOUT

VB ICIN ICOUT

~ Lmk mknm Reire:hSyud Em Parameters Work Sfalus mm oaApparnntNA) 1W FrequencytHI) W W Total ActiveNV) W Voltage Fhas: cream TotalReactlveNar) W CurrentFnaseOrderW [W TotalFowerFactor W NeutraICurremtAt W Phase A Phas: B Phase 0 , . VolkageM 0.00 0.00 107.21 15.21? 15:55: CurrenﬁA) 0.0000 0.0000 0.0000 ‘ ' Active PowerNV) W 0.0000 0.0000 Reactlve PowerNAR! 0.0000 0.0000 0.0000 Apparent PoweerA) 0.0000 0.0000 0.0000 M Q ICHDCHIF Power Factor 1.0000 1.0000 1.0000 CAD; POWPYSUPPIY Stews Losx Phasz Lost Fhasz Normal cow 20074722 0 50 Cummumcauunowcummamﬂﬁ cammumcale

Meter Overview

Step 3: Connect the RS-232 Cable

1. Connect the RS-232 cable from the energy meter to a Personal Computer (PC),

using either COM1, COM2, or COM6.

Step 4: Run the PC Calibration Software

After installing and running the PC energy meter software on a PC running a

Windows™ Operating System, and selecting the proper comm port for RS-232

communication, the following screen should show real-time meter results. The

following chapters include more detail on the firmware, calculation, and PC software.

FIGURE 1-3: “PM_Viewer” or Power Meter Viewer PC Software.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

NOTES:

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 2. Hardware Description

2.1 OVERVIEW

Figure 2-1 is the basic hardware block diagram of the MCP3909 / dsPIC33F 3-Phase

Energy Meter Reference Design. The hardware includes the dsPIC33F and ICD 2

interface, analog signal conditioning for 3-phase voltage/current inputs and current

using the MCP3909 Energy Meter IC, neutral current measurement using external

op-amp on-board dsPIC33F ADC, UART interface to PC, ICD2 interface for MCU

programming, and power supply circuits. Note there are two PCBs comprising this

energy meter, the power supply PCB, and the MCU/AFE PCB. Refer to Appendix

A. “Schematics and Layouts” for more information.

Three-phase voltage and current signals are connected to the meter through

transformers, and connected to the MCP3909 A/D converter through a simple signal

conditioning circuit. The MCP3909 device samples the signal and performs the

analog-to-digital conversion (ADC). The MCP3909 device sends the digital conversion

results to the dsPIC device via the SPI interface.

The MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design uses a quasi-syn-

chronous sampling algorithm via the dsPIC33F, therefore eliminating the need for

voltage zero-crossing detect and clock generating circuit, which are otherwise needed

in a synchronous sampling algorithm. The clock of the MCP3909 device is an active

external 3.2768 MHz crystal.

FIGURE 2-1: Hardware Block Diagram.

SPI

RS232

Phase A

Phase B

Phase C

MCP3909 MCP3909 MCP3909

dsPIC33FJ64GP206

CLK 3.2768

MHz

UART

Interface

+5V

Power Supply

ICD2

Interface

ADC

I/O

SPI

UART

Neutral

line CT

Gain

Control

Op Amp

+3.3V

Power Supply

\\\\\\

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

2.2 ANALOG FRONT END CIRCUITRY

For safety, current transformers are used between the voltage and current input signals

and the measurement module to isolate it from the 3-phase power supply.

The transformer used for the voltage path is a 1:1 transformer, SPT204B from Beijing

Singure Measurement & Control Technology Co., with non-linearity less than 0.1%, and

rated input/output current of 2mA/2mA.

The transformer used on the current side is a SPT254FK, from Yhehua Shanghai, with

rated input /output current of 20A/2 mA, non-linearity less than 0.1%, and linear range

of 0-20 A. See Appendix B. “Bill Of Materials (BOM)” for more information on the

input circuitry.

Using phase A as an example for the voltage signal path, a 150 kΩ (R1) resistor is used

before the CT to transform the signal to an appropriate current. After the CT, burden

resistors R125 and R126 are needed to transform the current signal to a differential volt-

age signal for the MCP3909 device to sample. Signals are coupled into the MCP3909

device's signal input port via R110 and R111. C111 and C112 are used to filter high-fre-

quency signals.

Using phase A as an example for the current signal path, transformation of the current

signal is similar to that of the voltage signal. The burden resistors R125/R126 and

R116/R117 are chosen to be 20Ω for the current channel and 100Ω for the voltage

channel after considering the following 3 factors:

• The MCP3909 device's differential voltage input range: 1V for voltage channel

and 0.705V for current channel

• Maximum current/voltage for the meter: rated current of 5A, maximum current of

20A, and maximum voltage of 300V)

• Transformer ratio for the current and voltage transformer.

A non-isolated voltage input circuit is included. In practice, a voltage divider network of

resistors is often used for sampling AC voltage input. This measuring method is

therefore included in the hardware design. In Figure 2-2, voltage divider resistors R3,

R4, and sampling resistor R1 construct a network for sampling AC voltage.

FIGURE 2-2: Input Signal Conditioning Circuit (Phase A).

1nF

1.0 kΩ

1nF

1.0 kΩ

20 Ω

MCP3909

CH0+

CH0-

CH1+

CTA-1 SCT220B

T103

R125

R126

R110

R111

C111

C112

1nF

1.0 kΩ

1nF

1.0 kΩ

100 Ω

SPT204B

R116

R117

R108

R109

C109

C110

150 kΩ

CURRENT

499 kΩ

1kΩ

VOLTAGE

33 nF

Jumper

VOLTAGE (Non-Isolated Option)

CTA-2

Hardware Description

2.2.1 Burden Resistor Temperature Coefficient

The high precision class 0.2S requirement for the energy meter makes it crucial to

select proper burden resistors for the output of the current transformers.

Metal film resistors with low inherent noise and temperature coefficient are ideal. Given

that the secondary current of the CT is I, then the input voltage of the MCP3909 device

is U = IR, where R is the resistance of R125 and R126 (Using Phase A as an example).

If the temperature varies by ΔT, and the temperature coefficient of sampling resistor R

is β ppm/°C, then the output voltage is:

EQUATION 2-1:

The voltage variation is:

EQUATION 2-2:

This relationship shows that the output voltage variation caused by temperature

variation is in proportion to the temperature coefficient of the burden resistor.

In addition, a smaller temperature coefficient benefits meter start stabilization after

startup. It takes a longer time for resistors with larger temperature coefficient to

stabilize. Therefore, accurate measurements would require a longer wait after

power-up. This affects the efficiency, or speed of meter calibration.

U'IR

β×

+()=

ΔUU'U–IΔTβ× R×× UΔT×β×== =

H mm r ‘F'AQ‘: J\ / #7 7—H \ / / \ / / \

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

2.3 ANALOG-TO-DIGITAL CONVERSION

This meter design uses Microchip's MCP3909 energy meter ICs. Small-signal current

inputs can be amplified by the programmable gain amplifier inside the MCP3909

device. The programmable range for the MCP3909's PGA is 16:1 V/V. The MCP3909

PGA gain can be configured by G0 and G1 (Pin 15 and 16 of the dsPIC33F).

The MCP3909 device's clock is provided by a 3.3768 MHz active crystal (for 50 Hz

system, see Appendix D. “50/60 Hz Meter Operation” for 60 Hz line frequency

information). The MCP3909 device's output data rate is 12.8 ksps. The clock lines and

MCLR lines of all 3 MCP3909 devices are connected together, which ensures that the

3 phases are strictly synchronous.

FIGURE 2-3: Clock Generation, Sampling Times and Calculation Frequencies.

MCP3909 MCP3909 MCP3909

X100

3.3768 MHz (50 Hz Version)

fSAMPLE1 = 12.8 ksps (Active Power)

tLINE_CYC

SDO DR

Phase A,B,C I & V Data

16 bits DR

tSAMPLE

MCLK input

DR Pulse

To dsPIC33F

SDO

IRQ IC1

x 6 ADCs

(Input Capture)

fSAMPLE2 = 6.4 ksps (Reactive Power, RMS Current / Voltage)

fSAMPLE3 = 3.2 ksps (Harmonic Analysis, Distortion)

Hardware Description

2.3.1 Samples And Processing

Input capture IC1 on the dsPIC33F is used to detect if A/D conversion is complete.

However, not all MCP3909 device samples are stored in the MCU, depending on the

parameter being calculated. The ADC conversion rate of the MCP3909 device is

determined by the frequency of the master clock (3.378 MHz for the case of a 50 Hz

line), and the output data rate is MCLK/256 or 12.8 ksps. After each conversion is

complete, a Data Ready signal is generated by the SDO of the MCP3909 device. The

signal is fed into IC1, allowing the Interrupt Service Routine (ISR) of IC1 to read the

data. When the MCP3909 device outputs data, it first sends an ADC result of the

voltage channel, then an ADC result of the current channel, with MSB first.

As noted, not all MCP3909 device samples are used for calculating all the parameters.

In practice, 6.4 ksps sampling rate is required, which means only 1 output data is used

for every 2 data sampled. For 50 Hz input signal, 6.4 ksps sampling rate will take 128

samples for each cycle. For example, the active power metering is computed based on

this condition.

But for other parameters for which precision is not critical, such as reactive energy,

voltage, current and frequency, the sampling rate may be reduced to save data storage

space and processing time. In this design, the 3.2 ksps sampling rate is used, which

means only 1 result is stored for every 4 ADC conversions.

After each conversion, a positive pulse with the width of 4 clock cycles is output by the

SDO pin of the MCP3909 device. IC1 is used to detect the falling edge of the pulse and

generate an interrupt for every 2 falling edges, i.e., 1 data is read for every 2 conver-

sions, thus realizing 6.4 ksps sampling rate.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

2.4 DSPIC33F HARDWARE CONNECTION AND PERIPHERAL USAGE

Table 2-1 is the pin allocation for the dsPIC33FJ64GP206 MCU.

TABLE 2-1: FUNCTIONAL ALLOCATION FOR dsPIC33F PINS

dsPIC

Pin Pin Function

Name

Corresponding Name

in Schematic

Diagram Functional Description

62, 1 RG14, RG15 G0A, G1A MCP3909's gain control for Phase A

2, 3 RC1, RC2 G0B, G1B MCP3909's gain control for Phase B

13, 12 RB3, RB4 G0C, G1C MCP3909's gain control for Phase C

14 RB2 CSA MCP3909's chip-select signal corresponding to Phase A

15 RB1 CSB MCP3909's chip-select signal corresponding to Phase B

16 RB0 CSC MCP3909's chip-select signal corresponding to Phase C

4, 5, 6 SCK, SDI, SDO SPI I/F Interface signal of SPI2. SPI interface operates under master

mode, used for the MCP3909 device communications

42 INT1 SDO SDO line of SPI interface, for detecting MCP3909's A/D

conversion complete flag

49-51 RD1-RD3 PULSE1, PULSE2,

PULSE3 PULSE1 is total phase active power pulse output, PULSE2 is

total phase reactive power pulse output. PULSE3's function is

to be determined.

61 RG0 AD_MCLR Master clear signal of 3 MCP3909 devices (tied together)

53 RC13, RC14 LED1, LED2 LED drive pins, can be used as energy pulse output indicator,

for meter calibration. Its function is similar to those of

PULSE1 and PULSE2

36, 37 SDA1 / SCL1 SDA/SCL I2C™ interface, used to read/write EEPROM externally

33, 34 U1TX / U1RX RF3/RF2 UART interface

33, 34,

35 SDO1/SDI1/SCK1 RF3/RF2/RF6 SPI1 interface, can be designed by customers, used for

communication with host MCU to obtain measurement results

and calibrate a meter. Its function is the same as UART

interface, but have a faster communication rate and higher

efficiency. SPI operates in slave mode. If UART interface is

used to communicate with host MCU, then this interface

cannot be used.

27 AN12 Current_N Detect neutral current

28 AN13 Ref_V Detect boost voltage of neutral current

17, 18 ICSPCLK, ICSP-

DAT ICSP I/F Online debugging/programming interface

7 MCLR MCLR Master clear input

Hardware Description

2.4.1 UART and SPI1 Interface

The UART and SPI1 interfaces are multiplexed. Through the UART or SPI1 interface,

the host MCU can communicate with the metering front-end to perform calibration or

obtain metering results. The SPI interface may also be used if high-speed data transfer

is desired. In this case, the SPI interface of the dsPIC device works in the slave mode.

The UART and SPI1 share a common pin, so only one of the two interfaces can be

used at a time. Since the reference design uses a PC to simulate the host MCU, the

UART interface is chosen as the communication interface. SPI and RS232 interfaces

are not isolated from the PC. A general-purpose transceiver device, MAX232, is used

for the UART interface.

2.4.2 Energy Pulse Output Interface

Three sets of outputs for energy measurement pulses are available in this design,

corresponding to the I/O pins of RD1-RD3. Two of them, output total active energy and

total reactive energy, respectively, and the other is not yet specified. Outputs are

isolated by a photo-electronic coupling device, U3. The photo-electronic coupler is

active when corresponding I/O pin is high.

In addition, the design also provides two sets of LED outputs for energy meter calibra-

tion. The output pins for these LEDs are RC13 and RC14. The LED is on when the

output is low. Figure 2-4 is the circuit of energy pulse output interface.

FIGURE 2-4: Energy Output Pulse Configuration.

RD3

RD2

RD1

RC13

RC14

1kΩ

R301

1kΩ

R301

1kΩ

R301

470Ω

R314

3.3V

470Ω

R310

3.3V

D303

D302

Total Active

Total Reactive

(not used)

Total Active

Total Reactive

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

2.4.3 Neutral Current Detection

Detection of neutral wire tampering is performed by the on-chip A/D of the dsPIC

device. The purpose of the detection is to prevent electricity theft, balance 3-phase

signals and detect electricity leakage. Since the precision is not critical, a dsPIC

on-chip A/D is sufficient.

Figure 2-5 shows the circuit for neutral current detection. The neutral input uses R128

for sampling. To bias the AC signals to the A/D measurement range, a 3.3V power

supply is divided by R130 and R129 and connected to the emitter-follower of the

MCP6002 device to output a boost voltage REV_V of 1.65V. The biased voltage is then

connected to the CT in series. The CT's sampling voltage is connected to Op-amp B of

the MCP6002 device via R127 as emitter-follower output, generating the sampling

voltage, Current_N, for the current. Both Current_N and 1.65V VREF signals are

sampled and measured by the dsPIC on-chip A/D.

FIGURE 2-5: Circuit of Neutral Line Detection.

R130

R129

Current_N

1.65V VREF

4.7 kΩ

R127

3.3V

U101_B

U101_A

470Ω

R128

T100 Secondary

Neutral Wire Input

Hardware Description

2.5 POWER SUPPLY

The power supply used in this design provides 3.3V and 5V. Since the energy meter for

a 3-phase 4-wire system is required to operate properly when any one phase is active,

a switching power supply module is used for convenience. T4 is the switching power

supply module.

Prior to the input of this module, additional protection circuitry is included with the meter

design. Figure 2-6 shows the input to the switching power supply module and the

additional filtering and protection circuitry. In Figure 2-6, R5 is the integrated ferrite

bead, C1, C4, C6, RV1, RV2 and RV3 are CBB capacitors and varistors. They are used

to improve anti-surge performance of the system.

FIGURE 2-6: Switching Power Supply Module (T4) and Additional Input Protection Circuitry.

JP5

JP4

JP6

4G1 5

Vo1 6

G2 7

Vo2 8

RV3RV1 RV2

4N5

COILS

12V

0.1u

0.1U C6

0.1u

JP6

Header 3

+C2

100uf

MCPHUI (SVSUIEW) 5V —:L’§ B CAP

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

An LDO is connected in series at the output of the switching power supply to obtain a

more stable power supply. Figure 2-7 shows this circuit. Microchip's MCP1701 device

and MCP1700 device, low drop-out high efficiency LDOs, are selected for use.

D301 is the power LED for the meter and is active when the meter is connected to the

proper line input voltage.

FIGURE 2-7: 5V and 3.3V LDO Modules.

C322

CAP C336

0.1uF

+C337

100uf

C323

CAP C324

CAP

+C338

100uf

+C339

47uF

D301

LED

R316

470

Vin

3Vout 2

Gnd1

U306

MCP1700(3.3V-SOT23)

J1 5V_IN

3.3V

L302

INDUCTOR

L301

INDUCTOR

Vin

2Vout 3

VSS

MCP1701(5V-SOT89)

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 3. Firmware

3.1 OVERVIEW

This section discusses the dsPIC firmware structure, peripheral resources, important

program flows, and explanations of project files included in the firmware zip files

included with the system. See Appendix D. “50/60 Hz Meter Operation” for

converting to 60 Hz code.

• Calculate all electrical parameters in frequency domain

• MCP3909 device communication

• Detect voltage/current phase order, and determine missing phases

• Generation imp/kWh power pulse

• UART communication

3.2 MAIN LOOP

The main loop of the entire dsPIC33F program is shown in Figure 3-1.

FIGURE 3-1: Main Loop Chart.

Main Program

Initialize on-chip

peripherals and variables

Process UART

comm. commands

Sampled 3 cycles? Compute elec.

parameters

Neutral data

acquisition complete?

Clear WDT

Compute

neutral line

current

Yes

and MCP3909 device

Calculation()

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

After system power-up, the MCU enters the initialization process, which includes

proper configuration of the I/O ports and on-chip peripherals (such as timer, UART, SPI

and IC). At the same time, the system control parameters can be loaded from the

external EEPROM and variables are all initialized.

Since most tasks of this system are accomplished through interrupts, only three tasks

are carried out in the system main loop, which are interpreting/processing UART

communication protocol, calculating parameters, and detecting neutral current. The

UART communication is performed in function UART_process(), the executing

frequency of which depends on the polling frequency of the upper computer.

Parameters are calculated by the function Calculation(), which is executed once every

3 cycles of the power grid. Neutral current is detected by function ComputeNeutral-

Current(), and computing is performed once every 16 cycles of the power grid.

+ >ﬁ¢ h 1"3 ¢ i d: L $ i ¢ $ $ i \, :

Firmware

3.3 CALCULATION() - CALCULATING ELECTRICAL PARAMETERS

All power parameters are calculated with the function Calculation(), which is executed

once every 3 cycles of the power grid. As shown in Figure 3-2, all calculations are

performed post DFT (direct fourier transform), in the frequency domain.

• RMS Voltage/current Of Each phase

• Phase Angle

• Measuring Line Frequency

• Active, Reactive, Apparent Power Of Each Phase

• Positive and Negative Active Power

• Positive/negative Reactive Power

• 4-quadrant Reactive Energy

• Total Active Power, Total Reactive Power, and Total Apparent Power

• Total Power Factor

• Voltage and Current Distortion Of Each Phase

• Voltage and Current Harmonic Contents Of Each Phase

FIGURE 3-2: Calculation() Flow

Chart.

Note: Algorithms for all calculations are shown in Appendix C. “Power

Calculation Theory”.

Calculate function

Select sync. window

function and

sine/cosine table

phase sequence 1~3

loop

Voltage signal and

sync. window process

DTF transformation

Calculate voltage

harmonic

Current signal and

sync. window process

DTF transformation

RMS value

Calculate current

harmonic

RMS value

Active/reactive

power calculation

and compensation

phase sequence 1~3

end

Calculate combined

power

Combined energy

accumulation

Calculate frequency,

determine phase

sequence

Update loop array

pointer and data

length

End of function

calculation

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

Each block can be categorized into one of three types of calculations:

1. Calculation for an individual phase

2. Calculation for all 3 phases

3. Calculation of power accumulation (Energy)

3.3.1 Process Quasi-Synchronization Window

The first blocks of the calculation flow are to determine how many samples to use for

the quasi-synchronization sampling algorithm. See Appendix C. “Power Calculation

Theory” for more information on this approach.

The firmware selects the proper quasi-synchronization window function (array of data)

and corresponding sine/cosine table according to the number of sampling points in

present current cycle.

The number of sampling points is obtained from the last calculation of frequency

function. As the line frequency fluctuates in slow motion and typically varies by a small

amount over three (3) line cycles, the period of line frequency measurements of the

previous cycle can be used to determine data length of sampling.

The quasi-synchronization window function is an array established in advance, and its

length is the same as that of the sampling data, which is obtained by the weight

coefficient multiplied by 32768. In this design, the method of quadrature by

complexification echelon is used, corresponding weight coefficient is calculated with

three (3) iterations. Three iterations implies that the length of the input original data is

equal to the number of sampling points in three cycles. The number of sampling points

in each cycle is usually different from the input signal cycle, but it will be close to an

integral multiple of the input signal cycle. For example, at a sampling rate of 3.2 ksps,

50 Hz input signal corresponds to 64 sampling points for each cycle, and 50.1 Hz input

signal would also be close to 64 sampling points for each cycle. Again, 51 Hz input

signal would be close to 63 sampling points for each cycle. Therefore, at different input

frequencies, the corresponding numbers of sampling points in each cycle are different.

Consequently, the corresponding quasi-sync window function and sine/cosine table

need to be established according to different numbers of sampling points. The

sine/cosine table is established by evenly dividing a cycle into a number of segments

equal to the number of sampling points, calculating corresponding sine/cosine values

and then multiplying the values by 32768. The purpose of the multiplication is to

change the original operation of floating point numbers into that of fixed-point numbers.

Adjustments will be performed in the final stage of calculation.

The processing of the original signal being processed by the quasi-synchronization

window function is actually a process of array multiplication, i.e. the original input signal

is multiplied with a corresponding array of window functions. It's accomplished by the

function qusi_syn_wnd(), which is written in assembly to take full advantages of DSP

features.

3.3.2 DFT Transformation

A Direct Fourier Transform (DFT) is performed on the collected sets of data. Process-

ing of the original signal by quasi-synchronization window can effectively reduce

spectrum leakage caused by non-entire-cycle sampling during DFT transformation.

The data length is not a power of 2, therefore, the FFT algorithm cannot be used in DFT

transformation. DFT transform is accomplished by function DFT(), which is written in

assembly to take full advantages of the DSP feature of accumulated multiplication.

Since an FFT algorithm cannot be used, and it takes longer to perform a DFT

calculation, this is the most time-consuming process in the entire system.

Firmware

3.3.3 Calculating RMS Voltage/Current

After the data set of either a voltage or current signal (of each phase), has been DFT

transformed, the voltage or current magnitudes of the different harmonics can then be

calculated. The total effective voltage or current (RMS) can be obtained by further

calculaton, by simply combining the results of the individual harmonics (including the

fundamental or the 1ST harmonic).

Computing the magnitude of the voltage or current is accomplished by function

ComputeMagnitude(). The result, called amplitude, is a long integer, and is the

squared magnitude of voltage or current. To speed up the computation, fixed-point

operation is used. The ComputeMagnitude() routine is written in assembly language.

After the magnitude is computed, there is an adjustment process which is based on a

floating-point operation. The limited number of computations will not affect the

operation speed, and will instead greatly improve precision.

Parameter ratio1 in the firmware is a coefficient related to the number of sampling

points (see Equation 2-2). Division is accomplished by a simple shift operation in

firmware. If the sampling cycle is not a power of 2, it cannot be accomplished by

shifting. However, division by shifting can be accomplished by multiplying a compen-

sating coefficient Coeff.data.linear.V_channel[]. This is the calibration coefficient for

ratio errors.

Since the current signal has a wide dynamic range, for small signals, the ADC output

data range is small and is limited by DSP's bit resolution (16-bit MCU). If division by

shift is used in the same way that is used for large signals in computation, precision

may be affected. Therefore, for computing magnitudes of small signals, ComputeS-

mallMagnitude() function is used instead. This function is similar to ComputeMagni-

tude(), the only difference being that the shift length is shortened in division operation,

and will be compensated during data adjustment. The computation precision will not be

affected as the data adjustment process uses float-point operation.

3.3.4 Calculating Harmonics

Computing harmonics is accomplished in assembly language, by the function Com-

puteHarmonic(). The computation is based on Equation C-62, in Appendix

C. “Power Calculation Theory”. The result is the ratio of the magnitude of K-th

harmonic to fundamental magnitude, and is given in a percentage.

3.3.5 Calculating Power

Computing power is accomplished in assembly language by the function Compute-

Power() based on Equation C-39 and Equation C-40 in Appendix C. “Power Calcu-

lation Theory”.

After the ComputePower() function is complete, an adjusting process for computed

power is required. First, the computed result is adjusted according to the gain of current

amplifier. Then the calibrating coefficient ratio2 is determined according to present

number of sampling points.

Additional compensation to the power calculation is required, for phase compensation.

This compensation is based on the present load current. The difference between signal

frequency and the central frequency is also taken into consideration. Consequently

computed power is compensated.

Note: Since the output of ComputeHarmonic() is the squared harmonic

magnitude, extraction of square root is needed in computation. The

calculated harmonic content is stored as a fixed-point number, and the

actual value stored is the harmonic content multiplied by 10.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

3.3.6 Active Energy Accumulation

Energy accumulation is done by calculating the total energy, which is the algebraic sum

of energy of each phase. Active energy is obtained by accumulating the multiplication

of voltage and current of each sample, which ensures the high accuracy of measure-

ment.

3.3.7 Reactive Energy Accumulation

The required measurement accuracy of reactive energy low, so in this design, it is

obtained by accumulating the product of the present measured reactive power and the

time interval between two measurements.

3.3.8 Output Pulse Generation

Refer to Section 2.4.2 “Energy Pulse Output Interface” for pulse output. To ensure

the uniformity of output pulses, the calculation is divided in the measurement cycle into

in a number of equal sections, and accumulate them. For simplification and lowering

computation complexity, a counter is used to substitute the process of accumulation.

The counter is only enabled when accumulated energy approaches to the threshold of

the pulse output.

3.3.9 Line Frequency Calculation

Frequency calculation is based on Equation C-52 and Equation C-53, in Appendix

C. “Power Calculation Theory”. The dsPIC33F collects 3-line cycles worth of data.

The first two cycles of data of all sampled data is analyzed, and then the frequency of

two successive cycles is used.

The data of two successive cycles are transformed via DFT for the fundamental, which

is accomplished by assemble function DFT_Fundamental(). This is followed by the

computation of the initial phase angle of the first two line cycles. Then the phase lag

and frequency offset of the two line cycles of signal can be calculated.

When measuring frequency, only the first two cycles of data are used. It must be

assumed the input frequency is 50 Hz and the chosen appropriate sine/cosine table to

carry out DFT transform for fundamentals of the 1st and 2nd cycles of data. See

Appendix D. “50/60 Hz Meter Operation” for 60 Hz firmware.

Frequency offset is calculated by determining the initial phase angle for each line cycle.

The greater the frequency offset, the greater the measurement error.

Since one of the 3 phases may be missing, if the voltage magnitude for phase A is less

than the threshold, it is necessary to switch to phase B. Consequently, if sufficient volt-

age magnitude of phase B is not detected, it is necessary to switch to phase C.

The basic algorithm for measuring line frequency is based on the method described in

Appendix A, Section C.4 “Measuring The Voltage/current Rms Value And Power

Using Quasi-synchronous Sampling Algorithm”.

Frequency will be measured once for every 3 times the data is sampled.

Firmware

3.4 ADC SAMPLING SCHEME FOR CALCULATIONS

The ADC conversion rate of the MCP3909 device is determined by the frequency of

master clock, MCLK, and the rate will be MCLK/256. After each conversion is complete,

a DataReady signal (4-CLK length) is generated by the SDO of the MCP3909 device.

The signal is fed into IC1 (Input Capture 1 on the dsPIC33F), allowing the Interrupt

Service Routine (ISR) of IC1 to invoke data-read function of the MCP3909 device.

When the MCP3909 device outputs data, it first sends the ADC result of the voltage

channel, then that of the current channel, with the MSB first.

The frequency of the master clock, MCLK, of the MCP3909 device is 3.2768 MHz, and

ADC outputs @12.8 ksps. In practice 6.4 ksps sampling rate is used in the program,

which means only 1 output data is used for every 2 data sampled. For a 50 Hz input

signal, a 6.4 ksps sampling rate will take 128 samples for each cycle. The active power

calculation is computed based on this condition.

The other parameters for which precision is not critical, such as reactive energy,

voltage, current and frequency, the sampling rate may be reduced to save data storage

space and processing time. In this design, the 3.2 ksps sampling rate is used, which

means only 1 result is stored for every 4 ADC conversions.

In the program, sampling and calculation are carried out concurrently, and data is

stored in the cyclic array in the dsPIC33F RAM. A calculation may be performed after

either 1 cycle, 2 cycles or 3 cycles of data are sampled, which can be configured in the

program. The user should note that frequent calculations will increase the measure-

ment precision at the price of system overhead and response speed, therefore making

proper tradeoffs based on practical requirement. In this design, 3 cycles of signals are

sampled before an AC electrical parameter calculation is performed. Refer to

Figure 3-3.

FIGURE 3-3: AC Signal Sampling alnd Computing.

3.4.1 Processing IC1 Interrupt

Input capture IC1 is used to detect if the A/D conversion is complete. After each

conversion, a positive pulse the width of 4 clock cycles is outputted by the SDO pin of

the MCP3909 device. IC1 is used to detect the falling edge of the pulse and generate

an interrupt for every 2 falling edges, i.e., 1 data is read for every 2 conversions, thus

realizing 6.4 ksps sampling rate.

In addition to reading the data of the MCP3909 device, the IC1 interrupt service routine

(ISR) also controls the energy pulse output generation. Energy pulse processing

consists of active/reactive energy pulse processing. For the pulses to be outputted

more uniformly, the clock resolution used to generate the pulses must be as high as

possible. The interval of the IC1 interrupt is 156.25 µs, therefore, the resolution

generated by the pulse can be up to 156.25 µs.

Sampling

Cycle n Sampling

Cycle n+1 Sampling

Cycle n+2 Sampling

Cycle n+3

Idle Idle Idle Calculate

n,n+1,n+2

Sampling

Cycle n+4

Idle

'rocessmg ﬁang edge m acme energy? Processmg nsmg edge 0| achve energy? Pmcessmg y lang edge 0| , eachve energy? .< processmg="" nsmg="" edge="" 0|="" achve="" energy?="">

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

The energy pulse processing program only begins when the level is close to outputting

pulse level. To simplify the process and shorten the ISR execution time, a counter is

used in place of the energy accumulation function for each pulse and to determine if a

pulse will be outputted. When the count is greater than the threshold of pulse output,

an energy pulse will be outputted, and the appropriate amount of energy will be sub-

tracted from the energy accumulating register. Output toggling will then be processed.

Once the width of the output pulse exceeds 80 ms, the pulse output will be turned off.

The program flow chart is shown in Figure 3-4.

FIGURE 3-4: IC1 Interrupt Service Routine.

ICI Interrupt Service

routine

Call MCP3909 data

read program

Processing

falling edge of

active energy?

Processing

rising edge of

active energy?

Processing

falling edge of

reactive energy?

Return

Yes

Processing

rising edge of

active energy?

Update pulse width

counter, if counter >

flip threshold, output

pulse and update

energy accumulation

Update pulse width

counter, if counter >

flip threshold, output

pulse and update

energy accumulation

Update pulse width

counter, if pulse

width > 80 ms, toggle

pulse output level.

End pulse output

process.

Update pulse width

counter, if pulse

width > 80 ms, toggle

pulse output level.

End pulse output

process.

Firmware

3.5 READING A/D DATA OF THE MCP3909 DEVICE

All three MCP3909 devices use the same clock source and reset signal, so all 6 A/D

channels of the 3 MCP3909 devices are synchronous. Only a single Data Ready (SDO)

signal of any of the MCP3909 device is required to read A/D data of the 3 phases in

turn. This module is invoked by IC1 interrupt triggered by the "data ready" signal on the

SDO of the MCP3909 device. IC1 is set to generate an interrupt for every two falling

edges. Therefore, only one of the two sampling data of the MCP3909 device is

read.The flow of reading the MCP3909 device's data is as follows:

• Retrieve all values of 3-phases, both current channel and voltage channel data.

Bits 0-15 of each phase data are voltage channel data, bits 16-31 are current

channel data

• Accumulate the active power of each phase. On every other interrupt, the current

and voltage values are stored into RAM in the cyclic sampling array

• Update the pointer of sampling array and length of sampling data. If the length of

sampling data is 3-line cycles long, set the sampling complete flag, and then the

calculation function Calculate() will be called by the main flow to start computing

all corresponding parameters.

FIGURE 3-5: Flow Chart of Read A/D Data.

Read MCP3909 data

Select phase A of

clear SPI flag

Even count

data read?

Read phase A data

and accumulate active

energy of phase A

Read phase B data

and accumulate active

energy of phase B

Read phase C data

and accumulate active

energy of phase C

End

Read phase A data,

accumulate active

energy of phase A

and save data to array

Read phase A data,

accumulate active

energy of phase A

and save data to array

Read phase A data,

accumulate active

energy of phase A

and save data to array

Update array pointer,

sample pass count

flag and data length

End of sampling of

this cycle?

Set data sampling

complete flag

Yes

The MCP3909 device,

\nitiahze MCPSQO?

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

3.5.1 Initialize and Configure MCP3909 Operation Mode

The task of this module is to enable the MCP3909 device to enter the "Channel Output"

mode. This design uses the "Channel Output" mode of the MCP3909 device. In this mode,

the current and voltage data channels measured by the ADC is sent through the

MCP3909 device's SPI port. To enable the MCP3909 device to enter the Channel

Output mode, certain instructions must be sent to the device via the SPI interface within

a specified time (32CLK) after resetting the MCP3909 device.

• Enable all MCP3909 devices: enable ADCS1, ADCS2 and ADCS3, and configure

MCU's SPI to 8-bit mode

• Reset the MCP3909 device through the RESET pin. The pin must be pulled low

for no less than 1 clock cycle of the MCP3909 device

• After the RESET pin is pulled high, wait for 4 clock cycles for the MCP3909 device

pin functions to reset

• Send Instruction 0x94 to the MCP3909 device through the SPI Interface

• Configure the SPI interface to 16-bit mode and strobe the MCP3909 device for

Phase A

FIGURE 3-6: Initializing the MCP3909 Device Flow Chart.

Initialize MCP3909

Strobe all

Reset the

Wait for 4 CLK cycles

Send instruction 0xac

Set SPI to 16-bit mode

Strobe phase A of

the MCP3909 device

End

MCP3909 devices

Firmware

3.6 COMMUNICATION OF UART INTERFACE

The UART interface is used to communicate with the upper computer (MCU or PC). Via

the UART interface, the upper computer reads the measured parameters of the power

grid, and may also send system parameters and calibration parameters to the target

board as well.

The communication interface is a bidirectional interface based on UART, using

master/slave half-duplex mode. The baud rate is 19,200 bps, with 1 start bit, 8 data bits

and 1 stop bit. Communication is done by frames with non-fixed-length frame structure,

definition of which is shown in Table 3-1. The Communication protocol is specified in a

master-slave structure. The system in this design is the slave, and the upper computer

is the master. The master sends commands to the slave, and slave responds to the

master.

Each command is defined in Chapter 6. “Meter Communications Protocol”.

TABLE 3-1: FRAME STRUCTURE OF COMMUNICATION PROTOCOL

3.7 RESOURCE CONFIGURATION

Details of the MCU resources used in this design and their configurations are listed in

Table 3-2.

Sync Field Command Type Data Length Data Field Checkout Byte End Byte

2 bytes 1 byte 1 byte N bytes 1 byte 1 byte

TABLE 3-2: CONFIGURATION OF MCU RESOURCES

Resource Name Interrupt

Priority Functional Description

System Clock Fcy = 29.4912M, provided by an external 7.3728 Mz timer through an inter-

nal PLL frequency doubler.

Timer Timer2 1 System clock, used for timing. Its cycle is 10 ms. The interrupt flag may be

set in the IRS. Used to extend the indication of timer. Also used to deal with

UART reception overtime.

Timer3 none Used to detect ADC's sampling synchronization of neutral current. After the

frequency of the power grid is measured, the period of TMR3 is adjusted

accordingly. 16 points are sampled by ADC for each cycle of power grid.

Interrupt TMR2 1 ditto

IC1 5 Driven by a 3.2768 MHz clock. The MCP3909 device can generate

12.8 ksps of data output.

Sampling input capture. An interrupt is generated for every two MCP3909

device samplings. 6.4 ksps sampling rate is realized.

In fact, active power is cumulated at 6.4 ksps sampling rate (128 sampling

points each cycle at 50 Hz), but other parameters are cumulated at 3.2 ksps

sampling rate

UART RX 2 Receive data of UART communication

UART TX 2 Transmit data of UART communication

ADC 2 Detect current of neutral line

SPI2 none Used in communicating with the MCP390X device - set the MCP390X

device's modes and read A/D results

SPI1 none Unused, but the interface is reserved and may be used to communicate

with upper computer in substitution of the UART interface

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

3.8 DESCRIPTION OF PROJECT FILES

TABLE 3-3: FILE DESCRIPTION

File Name Description

main.h

main.c Main program

global.h

global.c Mainly define important system macros, key data structures, and declare global variables.

MCP390x.h Declare macros, constants, local global variables, some of the global variables and functions

used in the MCP390X device.

MCP390x.c Functions involved with the MCP390X device, including set SPI, initialize the MCP390X device

and read data.

calcu.h Declare macros, constants, local global variables, some of the global variables and functions

used in calcu.c.

calcu.c Main module to calculate parameters, including calculate frequencies, current/voltage RMS,

power, power factors and energy, and analyze harmonics.

uart_comm.c Declare macros, constants, local global variables, some of the global variables and functions

used in uart.c.

uart.c Receive, transmit, process protocol and so forth for UART communication.

Calibrate.c Program for Ratio error calibration, power calibration and phase lag calibration, it stores and

initializes calibration data.

Calibrate.h Declare constants, local variables and global variables used in calibration.

Adc.c

Adc.h On-chip ADC operation, detecting the current of neutral wire.

I2Csubs.h

I2Csubs.c Control EEPROM of off-chip I2C interface.

interrupt.h Declare macros, constants, local global variables, some of the global variables and functions

used in interrupt.c.

interrupt.c Set interrupts and ISRs.

Asmcode.c Some assemble functions used in calculation.

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 4. Meter Calibration

4.1 INTRODUCTION

Meter calibration consists of using standard electrical power equipment that supplies

the power to the meter and calculates the error and correction factor at each calibration

point. This equipment must be accurate in order to calibrate the energy meter. The

supplied PC software is then used to send calibration commands and correction factors

down to the dsPIC33F, completing meter calibration.

Why Is Calibration Necessary?

An energy meter usually consists of errors due to transformers, VREF tolerance, ADC

gain errors, and other passive component errors. Energy meters are factory calibrated

before shipping to eliminate the impact from such elements and reduce the error. The

non-linearity and inconsistency of signals in the path of sampling circuit and A/D

conversion circuit cannot be ignored in high-accuracy measurement. The impact needs

to be corrected to improve measurement accuracy.

The calibration described in this chapter are calibrated with the help of the PC software

PM_Viewer, described in detail in the next chapter. To summarize the process, the

measurement error is fed into the software, and the data is then sent to the meter to via

the UART. The details of this procedure are detailed in the next chapter, "PC Software".

4.2 CURRENT/VOLTAGE CALIBRATION

Current and voltage calibration is a ratio error calibration from the upper computer by

sending commands and data for correction to the MCU. The dsPIC33F will call a

firmware module after receiving the command from the host PC. The flow is as follows:

1. Determine the phase to be calibrated and the magnitude of current and voltage

being applied to the meter, and read measurement (RMS) values of that channel.

2. Calculate the calibration coefficient of the ratio error by the ratio of standard value

received to the measured value.

3. Multiply the original coefficient by calibration coefficient and obtain the calibration

coefficient after correction.

4. Store the final calibration coefficient after correction into EEPROM.

Since the dynamic range of the voltage channel is usually very small, single-point

calibration is enough to meet the accuracy requirements for full range. However, the

dynamic range of the current channel is larger, and the transformer has different ratio

errors at different current loads.

The MCP3909 device’s current channel, CH0, contains a PGA with gain options of 1,

2, 8, 16. For high-accuracy energy meters, current ratio error needs to be segmented

and calibrated for different current loads. The ratio error calibration of current channel

uses a two-point calibration method. One point is calibrated when the load is at the

rated current (IB) and the PGA gain is 1. The second point is calibrated under small-sig-

nal input condition (0.1 IB) and the PGA gain is 16.

Note: Voltage and current calibration is a two step process using 100% and

10% IB.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

4.2.1 Current/Voltage Calibration Process

The process of calibration is as follows:

1. Supply the meter with balanced load, PF = 1.0, VCAL = 220V, IB = 5A.

2. Load the dsPIC33F with the proper correction factors. Automatically done using

the PC software. See Chapter 5. “PC Software”.

Repeat these following steps for the second point at 10% IB:

1. Set the three-phase balance input conditions PF = 1.0, VCAL = 220V, ICAL = 0.1 IB or

500 mA.

2. Load the dsPIC33F with the proper correction factors. Automatically done using

the PC software. See Chapter 5. “PC Software”.

If accuracy is not critical, the single-point calibration method can be used. The number

of calibration points can be defined in the header file of the program.

4.3 APPARENT POWER CALIBRATION

Apparent Power calibration function is implemented by the upper computer by sending

the commands. Before the power calibration process can be entered, power calibration

mode command needs to be sent first. The error data of the calibration workbench and

channel information to be calibrated are sent to the metering front-end. When the

front-end receives the command, it calls this module. The flow is as follows:

1. Determine the phase to be calibrated according to the parameters received.

2. Calculate new power calibration coefficient according to the error value received

and the measured value, together with the original power calibration coefficient.

3. Store the coefficient after correction into the EEPROM.

4.3.1 Apparent Power Calibration Process

The process of calibration is as follows:

1. Set the input condition as: Phase A PF = 1.0, VCAL = 220V, input current is the

current when region N is being calibrated, the voltage and current inputs of phase

B and C are zero.

2. Choose the energy pulse output to be the apparent power output mode Refer to

Chapter 6. “Meter Communications Protocol”. At this time, the energy pulse

is the accumulated multiplication of power and time.

3. Load the dsPIC33F with the proper correction factors. This is automatically done

using PC software. See Chapter 5. “PC Software”.

4. Repeat steps 1 - 3 for phase lag calibrations for all current regions of phase A.

5. Repeat the above steps for Phases B and C.

Note: At this time, the phase lag has not been calibrated, so when the input

PF = 1.0, the measured value of the reactive power isn't equal to zero.

Meter Calibration

4.4 PHASE LAG CALIBRATION

The phase lag calibration function is implemented by the upper computer by sending

the proper commands via the UART. When calibrating phase lag, error from the

calibration equipment and channel information to be adjusted are sent to the dsPIC33F

energy meter. When the front-end receives the command, it calls this module. The flow

is as follows:

1. Determine the phase to be calibrated according to parameters received.

2. Calculate new phase lag calibration coef. according to the error value received

and the measured value.

3. Store the coefficient after correction into the EEPROM.

This meter design supports single, two, and five point calibration for phase lag error

correction.

The purpose of phase lag calibration is to eliminate the impact of phase lag introduced

by the current transformer (CT), and voltage transformer (PT) over the power measure-

ment range.

The voltage transformer usually has a constant load, thereby introducing a phase lag

that varies insignificantly. The dynamic range of current is larger, and under different

current loads, phase lags caused by CT vary greatly. In order to meet the requirements

of measurement accuracy in the entire range, it is usually necessary to segment the

phase lag and calibrate.

In this design, current is partitioned into 5 regions.

TABLE 4-1: CURRENT REGIONS FOR PHASE CALIBRATION

The partition limit for the current region can be modified in the header file of the

program. If accuracy is not critical, single-point calibration and two-point calibration can

be used to improve the efficiency of meter calibration.

Single, Two, or Five Point Calibration

Single-, two- or five-point calibration method can be configured by modifying the

header file. When using the single-point calibration, the phase lag compensation

values of all regions are the same; When using two-point calibration, the compensation

values of region 1 and 2 (0-0.075 IB, 0.075 IB - 0.2 IB) are the same, and the phase lag

compensation values for region 3, 4 and 5 (0.2 IB - 0.75 IB, 0.75 IB - 1.5 IB, 1.5 IB -

4.0 IB) are the same.

Region Current Range

1 0 - 0.075 IB

2 0.075 IB - 0.2 IB

3 0.2 IB - 0.75 IB

40.75 I

B -1.5 IB

5 1.5 IB - 4.0 IB

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

4.4.1 Phase Lag Calibration Process

The process of phase calibration is as follow:

1. Setup input condition: Phase A, voltage input 220V, current input is the current

for region 1, voltage and current inputs of phase B and phase C are zero.

2. Load the dsPIC33F with the proper correction factors. This is automatically done

using the PC software. See Chapter 5. “PC Software”.

3. Repeat steps 1 and 2 for phase lag calibrations for all current regions of

phase A.

4. Repeat for Phases B & C.

Note: If the power metering error still can not meet the requirement, the meter can

be calibrated a few more times. When doing so, simply input a new error

value into the front-end of the meter.

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 5. PC Software

5.1 OVERVIEW AND INSTALLATION

The PC software “PM_Viewer” or “Power Meter Viewer” has two main functions: view

the calculated parameters and calibrate the meter. The PC software has seven output

display screens, or “work modes”, selected from the toolbar pull-down menu.

• Basic Parameters

• Phase A Harmonic

• Phase B Harmonic

• Phase C Harmonic

• Distortion Rate

•Harmonic Power

• Energy Accumulation

In addition, the PC software has four calibration screens, selected from the toolbar

pull-down menu.

• Reset All Calibration

• Linearity Calibration

• Apparent Power Calibration

• Phase Lag Calibration

5.1.1 System Required

• HDD space > 25 MB

• Microsoft Windows OS98 or later

• Hardware COM interface

5.1.2 Installation

1. Unzip PM_Viewer setup.zip.

2. Double click on setup.exe.

3. Finish the installation according the prompt.

4. To PM_Viewer.exe - Start -> Program -> Energy Meter ->PM_Viewer.exe.

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MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

5.2 ESTABLISH COMMUNICATION

1. Open PM_Viewer.

2. Click on Comm Port selection, and select the com port (com1, com2, or com3)

that you will use on the menu, noting the baud rate is 19200 bps in 1-8-1 format,

and can not be changed.

3. Click on the Link to establish communication with the demo. “Communication

OK!” will be displayed on the bottom, if communication is established.

FIGURE 5-1: Establising Communications.

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PC Software

5.3 BASIC PARAMETERS OUTPUT SCREEN

FIGURE 5-2: Basic Parameters Work Mode Screen.

5.4 PHASE A/B/C HARMONIC OUTPUT SCREEN

FIGURE 5-3: Phase N Harmonic Work Mode Screen.

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MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

5.5 DISTORTION RATE

FIGURE 5-4: Distortion Mode Screen.

5.6 HARMONIC POWER

FIGURE 5-5: Harmonic Power Work Mode Screen.

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PC Software

5.7 ENERGY ACCUMULATION

FIGURE 5-6: Energy Accumulation Work Mode Screen.

5.8 CALIBRATION STEP 1 - RESET ALL CALIBRATION

1. Select Reset All Calibration from the toolbar menu.

2. Meter Calibration Values are Reset.

FIGURE 5-7: Reset All Calibration Command.

n hem Eamhn me New. “has,“ gamma. 2“. LinsarityCalibration Region Select Phase selce¢ ﬁ 100% r: Phase A F 10% r Phase B r Phase I: Condimen- 3 phs balanceNoltage100%,Cuvrent100%, PF=I.0 channel Select : Vullage “ Current Resetlnnial Va‘ue standard Meter Value 22 set Close Wlndow znumm Work Status ‘Linearily Calibration 1 second 9 Mlcnncmn CADC

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

5.9 LINEARITY CALIBRATION

1. Select Channel, either Voltage or Current.

2. Select Phase A, B or C.

3. Select Region, either 100% or 10%.

4. Using a standard meter, supply the input conditions given here.

5. Enter the error recorded from the standard meter here.

6. Click the Set button.

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PC Software

5.10 APPARENT POWER CALIBRATION

1. Select Phase A, B or C.

2. Select Region n.

3. Using a standard meter, supply the input conditions given here.

4. Click the Set Apparent button.

5. Enter the error recorded from the standard meter here.

6. Click the Set button.

7. Repeat steps 2-5 for the different regions.

8. Repeat for other 2 phases.

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MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

5.11 PHASE LAG CALIBRATION

1. Select Phase A, B or C.

2. Select Region n.

3. Using a standard meter, supply the input conditions given here.

4. Enter the error recorded from the standard meter here.

5. Click the Set button.

6. Repeat steps 2-5 for the different regions.

7. Repeat for other 2 phases.

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Chapter 6. Meter Communications Protocol

6.1 INTRODUCTION

The UART interface is used to communicate with the upper computer (MCU or PC). Via

the UART interface, the upper computer reads the measured parameters of the power

grid, and may also send system parameters and calibration parameters to target board

as well.

The communication interface is a bidirectional interface based on UART, using

master/slave half-duplex mode. The baud rate is 19,200 bps, with 1 start bit, 8 data bits

and 1 stop bit. Communication is done by frames with non-fixed-length frame structure,

definition of which is shonw in Table 6-1. Communication protocol is specified in

master-slave structure. The system in this design is the slave, and the upper computer

is the master. The master sends commands to the slave, and the slave responds to the

master.

UART communication uses half-duplex mode. The data format is 8-1-1 and the rate is

19,200 bps. The PC is the host computer, and the target board is the slave.

There are 14 command strings that the meter uses. These command strings are

defined in Table 6-1

TABLE 6-1: COMMAND STRINGS

Command Description Command

Test Connection 0x41

Total Data Request 0x42

Harmonic Content, Phase A 0x43

Harmonic Content, Phase B 0x44

Harmonic Content, Phase C 0x45

Total Harmonic Distortion 0x46

Energy 0x47

Stop Energy Measurement and Clear Energy Values 0x48

Harmonic Power 0x49

Write Calibration Values to Meter 0x62

Write Phase Lag Calibration Values to Meter 0x63

Write Power Calibration Values to Meter 0x64

Write Energy Pulse Configuration - Active/Apparent 0x65

Reset All Calibration Values 0x66

Write Energy Pulse Constant 0x67

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

Variant-length frame structure is used and data communiate in bytes. The command

protocol structure is defined as following.

TABLE 6-2: TYPICAL PROTOTOL

• The START word has 2 bytes, which are 0x00, 0xFF ( PC to target board) or 0xFF,

0x00 (target board to PC)

• Command word is 1 byte which indicates the type of the command

• Data length word is 1 byte that indicates the length of data field

• The data field word has multiple byte(s) that varies with command types

• Checksum word is a single byte, whose content equals to the XOR value of all

bytes sent before it

• Stop word is 1 byte with the content of 0xE0

6.2 TEST CONNECTION COMMAND

This command is sent from the PC to the meter to setup and test the connection.

TABLE 6-3: PC TO METER (7 BYTES)

TABLE 6-4: METER RESPONSE (8 BYTES)

6.3 TOTAL DATA REQUEST

This is the main command retrieves all the calcuated data from the dsPIC33F. This

command gathers data from all 3 phases including total energy, power, and power

factor data.

TABLE 6-5: PC TO METER (7 BYTES)

TABLE 6-6: METER RESPONSE (104 BYTES)

START Command Data

Length Data Field Check Sum STOP

2 Bytes 1 Bytes 1 Byte N Bytes 1 Byte 1 Byte

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x41 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x42 0x02 0xA5, 0X5A XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x42 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x43 0x62 98 bytes XX 0xE0

Meter Communications Protocol

TABLE 6-7: METER RESPONSE, TOTAL REQUEST FRAME, DETAILED

DESCRIPTION

Data Field

Byte Name Value

1,2 Status See Definition Below

3-6 Frequency Float, 4 Bytes Total

7-10 Phase A Voltage Float, 4 Bytes Total

Phase B Voltage Float, 4 Bytes Total

Phase C Voltage Float, 4 Bytes Total

Phase A Current Float, 4 Bytes Total

Phase B Current Float, 4 Bytes Total

Phase C Current Float, 4 Bytes Total

Neutral Current Float, 4 Bytes Total

Active Power, Phase A Float, 4 Bytes Total

Reactive Power, Phase A Float, 4 Bytes Total

Apparent Power, Phase A Float, 4 Bytes Total

Power Factor, Phase A Float, 4 Bytes Total

Active Power, Phase B Float, 4 Bytes Total

Reactive Power, Phase B Float, 4 Bytes Total

Apparent Power, Phase B Float, 4 Bytes Total

Power Factor, Phase B Float, 4 Bytes Total

Active Power, Phase C Float, 4 Bytes Total

Reactive Power, Phase C Float, 4 Bytes Total

Apparent Power, Phase C Float, 4 Bytes Total

Power Factor, Phase C Float, 4 Bytes Total

Total Active Power Float, 4 Bytes Total

Total Reactive Power Float, 4 Bytes Total

Total Apparent Power Float, 4 Bytes Total

94-98 Total Power Factor Float, 4 Bytes Total

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

6.4 STATUS REGISTER

This register contains the gain register.

6.5 HARMONIC CONTENT COMMAND

TABLE 6-8: PC TO METER (7 BYTES)

TABLE 6-9: METER RESPONSE (134 BYTES)

R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0

CPO VPO PHC_S1 PHC_S0 PHB_S1 PHB_S0 PHA_S1 PHA_S0

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 7 CPO: Current Phase Order

1 = Problem Detected

0 =Normal

bit 6 VPO: Voltage Phase Order

1 = Problem Detected

0 =Normal

bit 5:4 PHC_S: Phase C Status

11 = High Votage

10 = No Input

01 = Low Voltage

00 = Normal

bit 3:2 PHB_S: Phase C Status

11 = High Votage

10 = No Input

01 = Low Voltage

00 = Normal

bit 1:0 PHA_S: Phase C Status

11 = High Votage

10 = No Input

01 = Low Voltage

00 = Normal

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x43 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x44 0x80 128 bytes XX 0xE0

Meter Communications Protocol

TABLE 6-10: HARMONIC ANALYSIS DETAILED DESCRIPTION

6.6 TOTAL HARMONIC DISTORTION (THD) COMMAND

TABLE 6-11: PC TO METER (7 BYTES)

TABLE 6-12: METER RESPONSE (29 BYTES)

TABLE 6-13: TOTAL HARMONIC DISTORTION DESCRIPTION

Data Field

Byte Description Value

1,2 Fundamential or 1st Harmonic, Voltage Content Unsigned Int, 2 bytes

3,4 2nd Harmonic, Voltage Content Unsigned Int, 2 bytes

5-56 3-31st Harmonic, Voltage Content Unsigned Int, 2 bytes

57,58 Total Voltage Harmonic Content (not including

Fundamental) Unsigned Int, 2 bytes, /

1000 * (100%)

59,60 Fundamential or 1st Harmonic, Current Content Unsigned Int, 2 bytes

61,62 2nd Harmonic, Current Content Unsigned Int, 2 bytes

63-126 3-31st Harmonic, Current Content Unsigned Int, 2 bytes

127,128 Total Current Harmonic Content (not including

Fundamental) Unsigned Int, 2 bytes, /

1000 * (100%)

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x46 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x47 0x18 24 bytes XX 0xE0

Data Field

Byte Description Value

1-4 Total Harmonic Distortion of Phase A Voltage Float, 4 Bytes Total

5-8 Total Harmonic Distortion of Phase B Voltage Float, 4 Bytes Total

9-12 Total Harmonic Distortion of Phase C Voltage Float, 4 Bytes Total

13-16 Total Harmonic Distortion of Phase A Current Float, 4 Bytes Total

17-20 Total Harmonic Distortion of Phase B Current Float, 4 Bytes Total

21-24 Total Harmonic Distortion of Phase C Current Float, 4 Bytes Total

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

6.7 START ENERGY MEASUREMENT COMMAND

TABLE 6-14: PC TO METER (7 BYTES)

TABLE 6-15: METER RESPONSE (42 BYTES)

TABLE 6-16: TOTAL HARMONIC DISTORTION DESCRIPTION

6.8 STOP ENERGY MEASUREMENT COMMAND

TABLE 6-17: PC TO METER (7 BYTES)

TABLE 6-18: METER RESPONSE (7 BYTES)

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x47 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x48 0x24 36 bytes XX 0xE0

Data Field

Byte Description Value

1-4 First quadrant reactive energy Float, 4 Bytes Total

5-8 Second quadrant reactive energy Float, 4 Bytes Total

9-12 Third quadrant reactive energy Float, 4 Bytes Total

13-16 Fouth quadrant reactive energy Float, 4 Bytes Total

17-20 Forward Reactive energy Float, 4 Bytes Total

21-24 Reverse Reactive Energy Float, 4 Bytes Total

25-28 Forward Active Energy Float, 4 Bytes Total

29-32 Reverse Active Energy Float, 4 Bytes Total

33-36 Reverse Active Energy Float, 4 Bytes Total

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x48 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x49 0x00 0 bytes XX 0xE0

Meter Communications Protocol

6.9 HARMONIC POWER COMMAND

TABLE 6-19: PC TO METER (7 BYTES)

TABLE 6-20: METER RESPONSE (54 BYTES)

TABLE 6-21: HARMONIC POWER MEASUREMENTS

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x49 0x00 0x00 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x4A 0x30 48 bytes XX 0xE0

Data Field

Byte Description Value

1-4 Fundamental Active Power Of Phase A Float, 4 Bytes Total

5-8 Fundamental Reactive Power Of Phase A Float, 4 Bytes Total

9-12 Fundamental Active Power Of Phase B Float, 4 Bytes Total

13-16 Fundamental Reactive Power Of Phase B Float, 4 Bytes Total

17-20 Fundamental Active Power Of Phase C Float, 4 Bytes Total

21-24 Fundamental Reactive Power Of Phase C Float, 4 Bytes Total

25-28 Harmonic Active Power Of Phase A Float, 4 Bytes Total

29-32 Harmonic Reactive Power Of Phase A Float, 4 Bytes Total

33-36 Harmonic Active Power Of Phase B Float, 4 Bytes Total

37-40 Harmonic Reactive Power Of Phase B Float, 4 Bytes Total

41-44 Harmonic Active Power Of Phase C Float, 4 Bytes Total

45-48 Harmonic Reactive Power Of Phase C Float, 4 Bytes Total

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

6.10 CALIBRATE METER VOLTAGE/CURRENT COMMAND

TABLE 6-22: PC TO METER (7 BYTES)

TABLE 6-23: METER RESPONSE (7 BYTES)

TABLE 6-24: CALIBRATION OF GAIN AND OFFSET VALUES

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x63 7 0x07 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x64 0 0x00 XX 0xE0

Data Field

Byte Description Value

1 Phase Select 0x01 = Phase A

0x02 = Phase B

0x03 = Phase C

2 Range Select 0x01 = 10%

0x02 = 100%

3 Channel Select 0x00 = Current

0x01 = Voltage

4-7 Correction Factor (Error Being Calibrated Out) Float, 4 Bytes Total

Meter Communications Protocol

6.11 CALIBRATE PHASE LAG COMMAND

TABLE 6-25: PC TO METER (12 BYTES)

TABLE 6-26: METER RESPONSE (7 BYTES)

TABLE 6-27: CALIBRATION OF PHASE LAG

6.12 CALIBRATE APPARENT POWER COMMAND

TABLE 6-28: PC TO METER (12 BYTES)

TABLE 6-29: METER RESPONSE (7 BYTES)

TABLE 6-30: CALIBRATION OF POWER

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x63 6 0x06 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x64 0 0x00 XX 0xE0

Data Field

Byte Description Value

1 Phase Select 0x01 = Phase A

0x02 = Phase B

0x03 = Phase C

2 Range Select 1-7

3-6 Correction Factor (Error Being Calibrated Out) Float, 4 Bytes Total

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x64 6 0x06 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x65 0 0x00 XX 0xE0

Data Field

Byte Description Value

1 Phase Select 0x01 = Phase A

0x02 = Phase B

0x03 = Phase C

2 Current Range Select 1-7

3-6 Correction Factor (Error Being Calibrated Out) Float, 4 Bytes Total

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

6.13 CALIBRATE ENERGY PULSE COMMAND

TABLE 6-31: PC TO METER (12 BYTES)

TABLE 6-32: METER RESPONSE (7 BYTES)

TABLE 6-33: CALIBRATION OF POWER

6.14 RESET ALL METER CALIBRATION VALUES COMMAND

TABLE 6-34: PC TO METER (12 BYTES)

TABLE 6-35: METER RESPONSE (7 BYTES)

TABLE 6-36: RESET METER OPTIONS

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x65 2 0x02 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x66 0 0x00 XX 0xE0

Data Field

Byte Description Value

1 Phase Select 0x01 = Phase A

0x02 = Phase B

0x03 = Phase C

2 Energy Output Mode 0x00 = Active Power

0x01 = Apparent Power

START Command Data

Length Data Field Check Sum STOP

0x00, 0xFF 0x66 4 0x04 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x67 0 0x00 XX 0xE0

Data Field

Byte Description Value

1 Command Type 0x55 - Reset All

0xA1 = Reset

0xA2 - Reset Power Calibration Only

0xA3 - Reset Phase Calibration

2 Phase Select 0x01 = Phase A

0x02 = Phase B

0x03 = Phase C

3 Current Range Select

4 Reserved

Meter Communications Protocol

6.15 CALIBRATE METER CONSTANT (ENERGY PULSE OUTPUT CONSTANT)

TABLE 6-37: PC TO METER (9 BYTES)

TABLE 6-38: METER RESPONSE (7 BYTES)

TABLE 6-39: ENERGY CONSTANT OPTIONS OPTIONS

START Command Data

Length Data Field Check Sum STOP

0x00, 0xFF 0x67 2 0x02 XX 0xE0

START Command Data

Length Data Field Check Sum STOP

0xFF, 0x00 0x68 0 0x00 XX 0xE0

Data Field

Byte Description Value

1-2 Energy Constant Range of 10064000 (Decimal)

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

NOTES:

6‘ MICROCHIP M

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Appendix A. Schematics and Layouts

A.1 INTRODUCTION

This appendix contains the following schematics and layouts for the MCP3909 /

dsPIC33F 3-Phase Energy Meter Reference Design.

• Power Supply Board Schematic

• Main Board Schematic - Page 1

• Main Board Schematic - Page 2

• Power Supply Board - Assembly Drawing

• Power Supply Board - Composite Drawing

• Main Board - Assembly Drawing

• Main Board - Composite Drawing

A.2 SCHEMATICS AND PCB LAYOUT

FIGURE A-1: LAYER ORDER

Top Layer

Bottom Layer

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

FIGURE A-2: POWER SUPPLY BOARD SCHEMATIC

1 2 34

321

ATitle

Number RevisionSize

Date: 30-Nov-2007 Sheet of

File: X:\AIPD Eval Boards\102-00011 thru 00020\102-00018\PCB Files (Protel )\PCB-R5\PM33_Drawn By:

150k

R11

150k

JP5

JP4

JP1

three phase voltage input

T3 SPT204B

T1 SPT204B

T2 SPT204B

2R = Vour*Rin/(Kpt*Vin)

JP6

Power supply for 3phs power meter

2.01 - 1

4G1 5

Vo1 6

G2 7

Vo2 8

DB-12CY

RV3RV1 RV2

4N5

COILS

12V

33N

R10

1K 1%

PC-

PC+

PB-

PB+

PA-

PA+

R12

PA+

PA-

PB+

PB-

PC+

PC-

JP3

Header 10

499K 1%

33N

PB-

33N

PA-

Jumper

0.1u

0.1U

0.1u

499K 1%

R13

499K 1%

R14

499K 1%

1K 1%

Jumper

JP6

Header 3

+C2

100uf

Schematics and Layouts

FIGURE A-3: MAIN BOARD SCHEMATIC - PAGE 1

123456

54321

Title

Number RevisionSize

Date: 30-Nov-2007 Sheet of

File: X:\AIPD Eval Boards\102-00011 thru 00020\102-00018\PCB Files (Protel )\PCB-R5\PM33_Drawn By:

Front-end of three Phase Power Meter Design

1.0

R113

100

R102

R100

1K C101

1nf

C104

1nf

R112

100

R121

R101 1K

C102

1nf

R122

C103

1nf

R103 1K

R115 100

R106

R104

1K C105

1nf

C108

1nf

R114

100

R123

R105 1K

C106

1nf

R124

C107

1nf

R107

R117

100

R110 1K

R108

1K C109

1nf

C112

1nf

R116

100

R125

R109 1K

C110

1nf

R126

C111

1nf

R111

2R = Vour*Rin/(Kpt*Vin)

2R = Vout/(Kct*Iin)

T101

SCT220B

T102

SCT220B

T103

SCT220B

T100

SCT220B

Current_N

R128

470

R127

4.7K

C100

1nf

Neutral line current detection

3.3V C128

0.1uF

R130

4.7K 1%

R129

4.7K 1%

3.3V

PCV-

PCV+

PCC+

PCC-

PBV-

PBV+

PBC+

PBC-

PAV-

PAV+

PAC+

PAC-

Current_N

1.65V

C121

1uf

C123

5V_IN

C122

AD_MCLR

C1260.1

C127

0.1

C117

C118

C119

C120

VCC

GND

7CLKOUT 8

X100

3.2768M Gain selection

G1 G0 Gain

0 0 1

0 1 2

1 0 8

1 1 16

C114

C113

C116

C115

C125

C124

DVDD

HPF

AVDD

CH0+

CH0-

CH1_

CH1+

MCLR

REFi/o

AGND

12 F1 13

F0 14

G1 15

G0 16

OSC1 17

OSC2 18

NC 19

NEG 20

DGND 21

HFo 22

Fo1 23

Fo0 24

U102 MCP3909

DVDD

HPF

AVDD

CH0+

CH0-

CH1_

CH1+

MCLR

REFi/o

AGND

12 F1 13

F0 14

G1 15

G0 16

OSC1 17

OSC2 18

NC 19

NEG 20

DGND 21

HFo 22

Fo1 23

Fo0 24

U103 MCP3909

DVDD

HPF

AVDD

CH0+

CH0-

CH1_

CH1+

MCLR

REFi/o

AGND

12 F1 13

F0 14

G1 15

G0 16

OSC1 17

OSC2 18

NC 19

NEG 20

DGND 21

HFo 22

Fo1 23

Fo0 24

U104 MCP3909

R131

4.7K

R132

4.7K

R133

4.7K

R134

4.7K

R135

4.7K

R136

4.7K

G0A

G1A

G0B

G1B

G0C

G1C

PCC+

PCC-

PCV-

PCV+

AD MCLR

PBC+

PBC-

PBV-

PBV+

PAC+

PAC-

PAV-

PAV+

AD MCLR

GAIN

G0A

G1A

SDI

SCK

G0B

G1B

G0C

G1C

GAIN

CSC

CSB

CSA

3905 CS

SDO

SPI I/F

AD_CLK

REF_V REV_V

AD_CLK

2-1

Jemmey Huang

FB3

500

FB2

500

AD_MCLR

FB1

500

R118

R119

R120

OutA

InA-

InA+

Vss

4InB+ 5

InB- 6

OutB 7

VDD 8

U101

MCP6002

CSC

SDI

SCK

SDO

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

FIGURE A-4: MAIN BOARD SCHEMATIC - PAGE 2

123456

54321

Title

Number RevisionSize

Date: 30-Nov-2007 Sheet of

File: X:\AIPD Eval Boards\102-00011 thru 00020\102-00018\PCB Files (Protel )\PCB-R5\PM33Drawn By:

R313

510

C340

0.1uf

S301

SW-PB

3.3V

Jemmey Huang

Front-end of three Phase Power Meter Design

1.0

AD CLK = Fac * SampleRate * Kad

F = 50Hz * 64 * 256 = 819.2 KHz

F = 50Hz * 128 * 256 = 1638.4 KHz

* 3905 clk range 1M to 4M C328

CON6

3.3V

C330

3.3V

C331

3.3V

C332

3.3V

C333

C334

R321

10k

ICSPDAT

ICSPCLK

MCLR

3.3V

C322

CAP

C336

0.1uF

+C337

100uf

C323

CAP

C324

CAP

+C338

100uf

+C339

47uF

D301

LED

R316

470

Vss

4SDA 5

SCL 6

WP 7

VCC 8

U309

24LC04B

3.3V

R311

R312

3.3V

C335

Vin

3Vout 2

Gnd

U306

MCP1700(3.3V-SOT23)

C342

0.1

C341

0.1 C344

0.1

C343 0.1

C1+

1V+ 2

C1-

C2-

T2OUT 7

C2+

4V- 6

R2IN 8

T1IN

T2IN

R1OUT

R2OUT

9R1IN 13

T1OUT 14

GND 15

VCC 16

U308

MAX232

3.3V

DB9

U1RX/SDI1

U1TX/SDO1

5V_IN

SCL

SDA

C329

RG15

AN16/RC1

AN17/RC2

RG6

RG7

RG8

MCLR

SS2/RG9

Vss

Vdd

AN15/RB5

AN4/RB4

AN3/RB3

AN2/RB2

PGC3/RB1

PGD3/RB0

PGC1/RB6

PGD1/RB7

AVdd

AVss

AN8/RB8

AN9/RB9

AN10/RB10

AN11/RB11

Vss

Vdd

AN12/RB12

AN13/RB13

AN14/RB14

AN15/RB15

RF4

RF5

RF3 33

RF2 34

INT0/RF6 35

SDA1/RG3 36

SCL1/RG2 37

Vdd 38

OSC1/RC12 39

OSC2/RC15 40

Vss 41

RD8 42

RD9 43

RD10 44

IC4/RD11 45

RD0 46

RC13 47

RC14 48

RD1 49

RD2 50

RD3 51

RD4 52

RD5 53

RD6 54

RD7 55

Vddcore 56

Vdd 57

RF0 58

RF1 59

RG1 60

RG0 61

RG14 62

RG12 63

RG13 64

U307

DSPIC33FJ128GP706

OSC1

OSC2

MCLR

ICSPDAT

ICSPCLK

C345

C346

X303

3.3V

GND

3.3V

GND

3.3V

R318 100

R317 100

R319 100

D303 LED

R314

470 3.3V

CSA

G0A

G1A

SCK

SDI

SDO

CSB

G0B

G1B

CSC

G0C

G1C

SPI I/F

CSA

G0A

G1A

CSB

G0B

G1B

CSC

G0C

G1C

GAIN

3909 CS

SCL

SDA

U1RX(SDI1)

U1TX(SDO1)

Current_N Current_N

SDO

3.3V

REF_V

SCK1

SCK2

SDO2

SDI2

U1RX/SDI1

U1TX/SDO1

SPI1_SCK

L302

INDUCTOR

L301

INDUCTOR

R303

C303

0.1uf

U303

TLP521-1

R302

C302

0.1uf

U302

TLP521-1

R301

C301

0.1uf

U301

TLP521-1

D302 LED

R310

470

AD_CLK AD_CLK

Output Pulse

1: active power -

2: active power +

3: Reactive power -

4: Reactive power +

5: TBD -

6: TBD +

2-2

AD_MCLR

MCLR

R309

100

R308

100

R307

100

R306

100

Vin

2Vout 3

VSS

U305

MCP1701(5V-SOT89)

Schematics and Layouts

FIGURE A-5: POWER SUPPLY BOARD LAYOUT - ASSEMBLY DRAWING

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

FIGURE A-6: POWER SUPPLY BOARD LAYOUT - COMPOSITE DRAWING

O on -- O .'.'.'.'. O o o —III\IIIIIHIIII\— .. . .. " ' ' ':. ...:-.. -'-' :' ‘ " I o :: = o c : : :IIIIIIIIIIII : : : ||||I||||||| . : :: Inmmm ' ::: mmmm ' E :: llll .- : _ _ _ II Illl .- O I ..' I O .0 . '0 . .0 . .0 0. g I. o O. . I. O O O

Schematics and Layouts

FIGURE A-7: MAIN BOARD LAYOUT - ASSEMBLY DRAWING

2111“

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

FIGURE A-8: MAIN BOARD LAYOUT - COMPOSITE DRAWING

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Appendix B. Bill Of Materials (BOM)

TABLE B-1: BILL OF MATERIALS - POWER SUPPLY (BOTTOM BOARD)

Qty Reference Description Manufacturer Part Number

3 C1, C2, C3 CAP 0.1UF 305VAC EMI SUPPRESS EPCOS Inc B32922A2104M

1 C4 CAP 470UF 25V ALUM LYTIC RADIAL Panasonic® - ECG ECA-1EM471

3 C5, C6, C7 DO NOT POPULATE — —

3 J4, J5, J6 CONN HEADER 3POS .100 VERT TIN Molex®/Waldom

Electronics Corp 22-23-2031

4 JP1, JP2, JP3,

JP4 HOOK-UP WIRE 18AWG STRAND RED Alpha Wire

Company 3055 RD005

4 JP1, JP2, JP3,

JP4 CONN RING TERM #6 18-22AWG Molex/Waldom Elec-

tronics Corp 19070-0040

1 JP6 CONN HEADER 3POS .156 VERT TIN Molex/Waldom

Electronics Corp 26-48-1035

1 JP6 CONN HOUSING 3POS .156 W/O RAMP Molex/Waldom

Electronics Corp 09-50-7031

3 JP6 CONN TERM FEMALE 18-24AWG TIN Molex/Waldom

Electronics Corp 08-50-0105

1 PCB RoHS Compliant Bare PCB, dsPIC33F

and MCP3909 3-Phase Energy Meter

(Power) Bottom Bd.

Microchip

Technology Inc. 104-00158

3 P4, P5, P6 CONN HOUS 3POS .100 W/RAMP/RIB

(Connects to Above) Molex/Waldom

Electronics Corp 22-01-3037

9 P4, P5, P6 CRIMP TERM FEMALE 22-30AWG TIN Molex/Waldom

Electronics Corp 08-65-0805

1 R1 Part of T1 Sanki —

1 R2 DO NOT POPULATE — —

6 R3, R4, R5, R6,

R7, R8 DO NOT POPULATE — —

3 R9, R10, R11 RES 150K OHM METAL FILM .50W 1% Vishay®/Phoenix

Passive

Components

5033ED150K0F12AF5

3 R12, R13, R14 DO NOT POPULATE — —

3 RV1, RV2, RV3 VARISTOR 300V RMS 14MM RADIAL EPCOS Inc S14K300E2

1 T1 3P AC-DC converter, 220V - 12V/5V Sanki DB-12CY220

3 T2, T3, T4 2mA/2mA Current transformer Xinge SPT204

3 W1, W2, W3 DO NOT POPULATE — —

Note 1: The components listed in this Bill of Materials are representative of the PCB assembly. The released BOM

used in manufacturing uses all RoHS-compliant components.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

TABLE B-2: BILL OF MATERIALS - TOP BOARD

Qty Reference Description Manufacturer Part Number

13 C100, C101, C102,

C103, C104, C105,

C106, C107, C108,

C109, C110, C111,

C112

CAP 1000PF 50V CERAMIC X7R

0805 Kemet® Electronics

Corp C0805C102K5RACTU

6 C113, C114, C115,

C116, C124, C125 CAP CER 10UF 16V X7R 1206 Murata Electronics®

North America GRM31CR71C106KAC7L

26 C117, C118, C119,

C120, C126, C127,

C128, C301, C302,

C303, C322, C323,

C324, C328, C330,

C331, C332, C333,

C334, C335, C336,

C340, C341, C342,

C343, C344

CAP .1UF 25V CERAMIC X7R 0805 Panasonic® - ECG ECJ-2VB1E104K

4 C121, C122, C123,

C329 CAP 1.0UF 10V CERAMIC X7R 0805 Kemet Electronics

Corp C0805C105K8RACTU

3 C337, C338, C339 CAP 470UF 25V ALUM LYTIC

RADIAL Panasonic - ECG ECA-1EM471

2 C345, C346 CAP 22PF 50V CERM CHIP 0805

SMD Panasonic - ECG ECJ-2VC1H220J

3 6" Wire Thru CT HOOK-UP WIRE 16AWG STRAND

RED Alpha Wire

Company 3057 RD005

6 CT Wire terminals CONN RING TERM #6 18-22AWG Molex/Waldom

Electronics Corp 19070-0040

1 D301 LED 3MM ALGAAS RED CLEAR LITE-ON INC LTL-4266N

1 D302 LED 3MM GREEN CLEAR LITE-ON INC LTL-4236N

1 D303 LED 3MM YELLOW CLEAR LITE-ON INC LTL-4256N

3 FB1, FB2, FB3 FERRITE SMT luying STBL2012-121

1 J1 CONN HOUSING 3POS .156 W/O

RAMP Molex/Waldom

Electronics Corp 09-50-7031

1 J1 CONN TERM FEMALE 18-24AWG

TIN Molex/Waldom

Electronics Corp 08-50-0105

1 J1 HOOK-UP WIRE 22AWG STRAND

RED Alpha Wire

Company 3051 RD005

1 J1 HOOK-UP WIRE 22AWG STRAND

BLACK Alpha Wire

Company 3051 BK005

1 J2 CONN MOD JACK 6-6 VERT PCB

50AU Tyco

Electronics/Amp 5520258-3

1 J3 CONN HEADER 6POS .100 VERT

TIN Molex/Waldom

Electronics Corp 22-27-2061

1 J4 CONN HEADER 4POS .100 VERT

TIN Molex/Waldom

Electronics Corp 22-27-2041

1 J5 DB9 Female vertical Tyco

Electronics/Amp 747091-2

3 J6,J7 & J8 CONN HOUS 3POS .100

W/RAMP/RIB (Connects to J4,J5 & J6

of Lower Board)

——

9 J6,J7 & J8 CRIMP TERM FEMALE 22-30AWG

TIN Molex/Waldom

Electronics Corp 08-65-0805

Note 1: The components listed in this Bill of Materials are representative of the PCB assembly. The released BOM

used in manufacturing uses all RoHS-compliant components.

Bill Of Materials (BOM)

3 J6,J7 & J8 HOOK-UP WIRE 22AWG STRAND

GREEN Alpha Wire

Company 3051 GR005

3 J6,J7 & J8 HOOK-UP WIRE 22AWG STRAND

RED Alpha Wire

Company 3051 RD005

3 J6,J7 & J8 HOOK-UP WIRE 22AWG STRAND

BLACK Alpha Wire

Company 3051 BK005

2 L301, L302 60ohm bead Jones B60

1 PCB RoHS Compliant Bare PCB,

dsPIC33F and MCP3909 3-Phase

Energy Meter (Power) Bottom Bd.

— 104-00159

17 R100, R101, R102,

R103, R104, R105,

R106, R107, R108,

R109, R110, R111,

R301, R302, R303,

R311, R312

RES 1.00K OHM 1/8W 1% 0805 SMD Panasonic - ECG ERJ-6ENF1001V

12 R112, R113, R114,

R115, R116, R117,

R307, R308, R309,

R317, R318, R319

RES 100 OHM 1/8W 1% 0805 SMD Panasonic - ECG ERJ-6ENF1000V

3 R118, R119, R120 RES 10.0 OHM 1/8W 1% 0805 SMD Panasonic - ECG ERJ-6ENF10R0V

6 R121, R122, R123,

R124, R125, R126 RES 20.0 OHM 1/8W 1% 0805 SMD Panasonic - ECG ERJ-6ENF20R0V

7 R127, R131, R132,

R133, R134, R135,

R136

RES 4.7K OHM 1/8W 5% 0805 SMD Panasonic - ECG ERJ-6GEYJ472V

4 R128, R310, R314,

R316 RES 470 OHM 1/8W 5% 0805 SMD Panasonic - ECG ERJ-6GEYJ471V

2 R129, R130 RES 4.70K OHM 1/8W 1% 0805 SMD Yageo Corporation 9C08052A4701FKHFT

1 R313 RES 510 OHM 1/8W 5% 0805 SMD Panasonic - ECG ERJ-6GEYJ511V

1 R321 RES 10.0K OHM 1/8W 1% 0805 SMD Panasonic - ECG ERJ-6ENF1002V

1 S301 SWITCH TACT 6MM MOMENTARY

250GF E-Switch TL1105BF250Q

1 X100 3.2768Mhz Crystal Koan DIP-8-3.2768M

1 X303 7.3728Mhz Crystal Koan HC-49S-SMD-7.3728M

1 U305 2uA Low Dropout Positive Voltage

Regulator Microchip

Technology Inc MCP1701T-5002I/MB

1 U306 Low Quiescent Current LDO Microchip

Technology Inc MCP1700T-3302E/TT

1 U307 High-Performance, 16-bit Digital Sig-

nal Controllers Microchip

Technology Inc dsPIC33FJ128GP206

1 U308 IC DRVR/RCVR MULTCH RS232

16SOIC Texas Instruments MAX3232CDR

1 U309 4K I2C™ Serial EEPROM Microchip

Technology Inc 24LC04B-E/SN

3 U102, U103 U104 Energy Metering IC with SPI Interface

and Active Power Pulse Output Microchip

Technology Inc MCP3909-I/SS

1 U101 1MHz, Low Power Op-Amp Microchip

Technology Inc MCP6002-I/SN

3 T101 T102, T103 5A/5mA Current transformer Xinge SCT954F

1 T100 " DO NOT POPULATE — —

TABLE B-2: BILL OF MATERIALS - TOP BOARD

Qty Reference Description Manufacturer Part Number

Note 1: The components listed in this Bill of Materials are representative of the PCB assembly. The released BOM

used in manufacturing uses all RoHS-compliant components.

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

NOTES:

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Appendix C. Power Calculation Theory

C.1 OVERVIEW

This MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design is unique in that

all calculations are done in the frequency domain. This is easily realized using the DSP

engine core of the advanced 16-bit MCU, the dsPIC33F. In addition to performing direct

fourier transforms (DFTs) on all the input channel measurements, an additional

firmware function is included, quasi-synchronous sampling.

C.2 SYNCHRONOUS SAMPLING AND QUASI-SYNCHRONOUS SAMPLING

The fundamentals of quasi-synchronous sampling and corresponding methods for

measuring AC electrical parameters are discussed in this section. Typically, a

synchronous sampling method is used for measuring electrical parameters. The

method requires synchronization between sampling intervals and power grid

frequency. For these types of meter designs, an external hardware PLL circuit is used

to track power grid frequency, and the clock of the MCP3909 device is automatically

updated to change the sampling frequency. Since the PLL output frequency drops

behind the power grid frequency, a synchronous error exists in the system, and fully

synchronous sampling is hard to achieve. In addition, as non-sine waves exist in the

power grid, which may affect zero-crossing detection, when such conditions worsen, it

may cause PLL failure, preventing the system from working normally.

For the MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design presented

here, the dsPIC33F performs additionall calculations that eliminates the need for a

costly external PLL circuit. This quasi-synchronous sampling method has an

advantage in the engineering practice, which actually is periodic sampling, without

synchronizing with the power grid frequency. Therefore, the zero-crossing detection

and PLL circuit can be reduced to lower the hardware complexity. The tradeoff is the

increased software requirements of the system, easily realized using the powerful

dsPIC33F.

For DFT or FFT harmonic analysis of periodic signals, a Fourier transform may only

bring accurate spectrum analysis when the sampling points satisfy N > 2M for each line

cycle and strict synchronous sampling is realized. (Where M is the maximal harmonic

order of periodic signals, and N is the number of samples per line cycle).

Otherwise, if N ≤ 2M, it will cause spectrum aliasing. In addition, if strict synchronous

sampling cannot be realized, spectral-leakage will occur (the Hurdle Effect). However,

in the quasi-synchronous sampling method emplyed here, strict synchronization

between sampling intervals and the period of sampled signal is not guaranteed but is

overcome through post-processing and iteration of the collected data. To reduce the

error caused by this problem and to obtain better accuracy when measuring the

fundamental and harmonics of higher orders, an increase in the number of iterations

when processing data to improve accuracy is performed.

The iterations can effectively reduce the impact of synchronization error over the mea-

surement accuracy, and is one of the methods to realize accurate measurement of the

frequency and harmonics under steady-state conditions.

faaﬂ ayﬁa

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

FIGURE C-1: Quasi Synchronous Sampline.

C.2.1 Basic Idea of Quasi-Synchronous Sampling

Assuming that the average of a periodic signal in one cycle is g(t),

EQUATION C-1:

Make t = x/

, then,

EQUATION C-2:

where f(x) = g(x/

), and the period is 2π.

If the entire period sampling cannot be realized while a sampling frequency deviation

Δ exists, then:

EQUATION C-3:

We have:

EQUATION C-4:

The value of F1(α) is a function of

and also a function with 2π as its perod. The

non--synchronous sampling error E = f(x)- F1(α).

As F1(α) is function with 2

as its period, its value may be averaged through integration

within the range of 0-2

, and it can be deduced that f(x) = F1(α).

T≠N*Ts

gt() 1

---g

∫t()dt

⋅

---g

TO T+()

∫t()dt

⋅

gt() 1

------ fx()xd

∫

⋅

fx()==

fx() 1

πΔ

-----------------fx()x

πΔ

+()

∫

⋅

πΔ

-----------------fx()x

πΔ

++()

∫

⋅≠≠

() 1

πΔ

-----------------fx()xd

πΔ

++()

∫

⋅

Power Calculation Theory

Assuming that the integral starts at β, then:

EQUATION C-5:

Likewise, as strict integration cannot be realized in the entire cycle, so:

EQUATION C-6:

Similarly, the integral value of above equation is related to β with 2π as its period, let’s

denote it as F2(β). If it won't confuse people, we'll write F1(α) and F2(β) as F1(x) and

F2(x), and a recurrence formula can be obtained as the following:

EQUATION C-7:

It can be proved that,

EQUATION C-8:

In practical applications, it is necessary to sample the continuous analog signals and

process the data obtained with discrete algorithms. The quasi-synchronous recursive

process mentioned above can be expressed as follows:

For Equation C-4, the integral interval [x0,x

0+nx(2π + Δ)] whose width is nx(2π+Δ)

can be divided equally into nxN sections, which results in nxN+1 sampled data,

f(xi), (i=0,1,...,nxN), and we can iterate as follows:

fx() F1

() 1

------ F1

()

+()

∫

⋅

fx() F1

() 1

πΔ

-----------------F1

()

πΔ

++()

∫

⋅≠

() 1

πΔ

-----------------Fn1–x()xd

πΔ

++()

∫

⋅

()

∞

–

lim f x()=

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

First iteration:

…

Second iteration:

…

F011

i0=

∑

---------------

i0=

∑fx

()

⋅⋅

F111

ρi

i1=

N1+

∑

----------------ρi

i1=

N1+

∑fx

()⋅⋅=

F1n1–()N

in1–()N

∑

----------------------------------

ifx

()

⋅

in1–()N

∑

⋅

F021

i0=

∑

---------------

iFi1

⋅

i0=

∑

⋅

F121

i1=

N1+

∑

----------------

i1=

N1+

∑Fi1

⋅⋅

F2n2–()N

in2–()N

Nn1–()

∑

----------------------------------

in2–()N

Nn1–()

∑Fi1

⋅⋅

Power Calculation Theory

Third iteration:

…

F031

i0=

∑

---------------

i0=

∑Fi2

⋅⋅

F131

i1=

N1+

∑

----------------

i1=

N1+

∑Fi2

⋅⋅

F3n3–()N

in3–()N

Nn2–()

∑

----------------------------------

in3–()N

Nn2–()

∑Fi2

⋅⋅

\ |

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

N-th iteration:

Where ρi is the weight coefficient which is decided by the digital quadrature formula.

Complex rectangular quadrature algorithm or complex trapezoidal quadrature

algorithm is usually used in quasi-synchronous sampling.

Figure C-2 shows a 3-cycle interative process.

FIGURE C-2: 3-Cycle Iterative Process.

In practical applicatons, a frequency offset Δ is usually small, and good results may

usually be obtained through 3-5 iterations.

As mentioned above, the iterative process will result in a group of weight coefficients

ηi, called weight coefficients of quasi-synchronous algorithm, they may be deduced

from the numeric quadrature formula. The relationship between the iterative result and

original data is shown in Equation C-9.

EQUATION C-9:

F0n1

i0=

∑

---------------

i0=

∑Fin1–

⋅⋅

F01

F02

F03

Original data

First Iteration

Second Iteration

Third Iteration

F12F22...... FN2

F11F21...... FN1F1N+1 F1N+2 ...... F12N

f1f2...... fNfN+1 fN+2 ...... f2N f2N+1 f2N+2 ...... f3N

F0n1

i0=

∑

----------------

ifx

()

⋅

i0=

∑

⋅

------

ifx

()

⋅

i0=

∑

⋅

Rifx

()

⋅

i0=

∑

72 I] DEM I DEIZ \ DDS \ [IDA I DDS DUE

Power Calculation Theory

Where:

EQUATION C-10:

Equation C-10 is called the quasi-synchronous window function. After determining the

sampling points, the number of iterations and numerical quadrature method, the

coefficients of quasi-synchronous window function will become definite, and a

quasi-synchronous window function arrays may be established in advance.

Using the quasi-synchronous window function to carry out the weighted process of the

original data is equivalent to carrying out data synchronization one time, and the

algorithm realization is also very simple that only a multiplication of the original data and

quasi-synchronous window function arrays is required. After processing, the new

periodic signal will have the same period and frequency components as the original

signal, and the synchronization error of the new signal becomes smaller.

Figure C-3 is a schematic of the quasi-synchronous window function characteristics in

the time domain and data processing. In Figure C-3, the red curve is the characteristic

of the window function, and the blue curve is input signal, and the green curve is the

output signal.

FIGURE C-3: Quasi-Synchronous Window Function Characteristics Curve and Data

Processing.

Ri1

------

⋅

（

i = 0 ~ n x N

）

Amplitude

Sampling point (1-193) Time 3.2 ksps

Window function

Raw data

Data processed

r A“, n

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.3 THE HARMONIC ANALYSIS ALGORITHM OF QUASI-SYNCHRONOUS

SAMPLING

Periodic signal can be expressed as trigonometric Fourier series or exponential Fourier

series. A periodic signal with a period of T can be expressed as :

EQUATION C-11:

where:

EQUATION C-12:

EQUATION C-13:

or as:

EQUATION C-14:

where the relationship between ak, bk，ck and ϕk is:

EQUATION C-15:

EQUATION C-16:

EQUATION C-17:

ft()

-------

⋅⋅

()cos

⋅⋅

()cos+()

k1=

∞

∑

ak2

---ft()

∫k

⋅⋅

()dtcos

⋅⋅

bk2

---ft()

∫k

⋅⋅

()sin dt

⋅⋅

ft() a0ckk

⋅⋅

()sin

k1=

∞

∑

ckak

2bk

-----atan=

akck

sin=

Power Calculation Theory

EQUATION C-18:

Make g(t) = f(t) • cos(K•ω•t), it can be proved that g(t) is also a periondic function with T

as its period. Averaging g(t) in the range of [0 ~ T] results in:

EQUATION C-19:

So ak = 2 × g(t). Therefore, ak can be obtained if only g(t) can be calculated.

EQUATION C-20:

EQUATION C-21:

Where N, n and ηi are constants. The equation may therefore be written as:

EQUATION C-22:

EQUATION C-23:

Where:

EQUATION C-24:

bkck

cos=

gt() 1

---ft()

∫k

⋅⋅

()dtcos

⋅⋅

ak2g t() 2

------

igi

⋅

i0=

∑

⋅

------ ηifik2π

------ i⋅⋅

⎝⎠

⎛⎞

cos⋅⋅

i0=

nN×

∑

⋅=

bk2

------

ifik2

------ i

⋅⋅

⎝⎠

⎛⎞

sin

⋅⋅

i0=

∑

⋅

akIifik2

------ i

⋅⋅

⎝⎠

⎛⎞

cos

⋅⋅

i0=

∑

bkIifik2

------ i

⋅⋅

⎝⎠

⎛⎞

sin

⋅⋅

i0=

∑

Ii2

------

1R12

⋅

= i 0nN

×∼

=()

1+ 24

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.4 MEASURING THE VOLTAGE/CURRENT RMS VALUE AND POWER USING

QUASI-SYNCHRONOUS SAMPLING ALGORITHM

From Equation C-11, a periodic voltage can be expressed as:

EQUATION C-25:

So the voltage fundamental and the voltage of each harmonic can be expressed as:

EQUATION C-26:

From Equation C-25, the fundamental voltage and voltage of each harmonic can also

be expressed as:

EQUATION C-27:

Where:

EQUATION C-28:

EQUATION C-29:

The voltage RMS value of each harmonic, then can be expressed as shown in

Equation C-31 with its initial phase angle shown in Equation C-29.

EQUATION C-30:

Ut() Ua0

-----------u

ak k

⋅⋅

()cos ubk k

⋅⋅

()sin+()

k1=

∞

∑

Ukt() uak k

⋅⋅

()ukk

⋅⋅

()sin+cos=

Ukt() uck k

⋅⋅ ϕ

+()sin=

uck uak2ubk2

uak

ubk

-------atan=

Uk1

-------uck

uak2ubk2

----------------------------

⋅

Power Calculation Theory

The relationship between uak, ubk and Uk can be expressed as:

EQUATION C-31:

EQUATION C-32:

Total effective voltage can be expressed as:

EQUATION C-33:

Similarly, the effective values and initial phase angles of fundamental current and

current of each other harmonic can be expressed as:

EQUATION C-34:

EQUATION C-35:

The relationship between iak, ibk and Ik can be expressed as:

EQUATION C-36:

EQUATION C-37:

Total current RMS can be expressed as:

EQUATION C-38:

uak 2U

sin

⋅⋅

ubk 2U

cos

⋅⋅

Utotal Uk2

k0=

∞

∑

Ik1

-------ick

⋅

iak2ibk2

-------------------------

iak

ibk

------atan=

iak 2I

sin

⋅⋅

ibk 2I

cos

⋅⋅

Itotal Ik2

k0=

∞

∑

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

According to the definition of power measurement, the active power and reactive power

of the fundamental and each other harmonic can be expressed as:

EQUATION C-39:

EQUATION C-40:

Substituting Equation C-31, C-32, C-33 and C-37 into Equation C-39 and C-40, the

power of each harmonic component can be obtained with the following:

EQUATION C-41:

EQUATION C-42:

Total active power and reactive power can be expressed as:

EQUATION C-43:

EQUATION C-44:

PkUkIk

–()cos=

---UkIk

⋅ϕ

sin

cos

cos+()=

QkUkIk

–()sin=

---UkIk

⋅ϕ

sin

cos

sin–()=

Pk1

---uakiak ubkiik

+()

⋅

Qk1

---uakiak ubkiik

–()

⋅

Ptotal Pk

k0=

∞

∑

Qtotal Qk

k0=

∞

∑

Power Calculation Theory

C.5 MEASURING FREQUENCY

There are many ways to measure frequency, with the most common being counting the

signal cycle. In this method, a counter increments each time a zero-crossing is

detected. Based on the counts, the width of a cycle can be measured. If the zero-cross-

ing is accurate and the counter precision is high enough, cycle counting can be a

simple and practical method. But if the input signal has large harmonic components,

causing distortion around zero-crossing, then this approach may produce large errors.

Another method is to analyze and process the sampled data and calculate the frequen-

cies. Analysis may be carried out in time domain, such as digital differential ND and

interpolation method; or may be carried out in frequency domain after DFT transforma-

tion, such as gravity center method, spectrum zoom method and phase difference

method, among which the phase difference method is the most common one. It is not

sensitive to signal distortion around zero-crossing points.

The basic idea of the phase difference method is: if the rough range of to-be-measured

signal frequency is known, then we may assume a frequency that is close to the actual

frequency and then acquire an array of samples based on the assumed frequency. In

the sampled data, the phase of the 1st cycle and the subsequent N-th cycle are meau-

red and their difference may be calculated. Then the phase difference may be used to

calculate the difference between the actual freqency and the assumed frequence, thus

figuring out the actual frequency.

If the frequency f0 to be measured is known to be a definite value f, i.e., f0=f+Δf,

Δf<< f, then from Equation C-27, the fundamental signal can be expressed as:

EQUATION C-45:

If:

EQUATION C-46:

EQUATION C-47:

EQUATION C-48:

U1t() uc1

⋅

()sin uc1 2

f0t

+()sin==

---=

ua2

---U1t()

t()cos td

∫

⋅

---uc1 2

f0t

+()2

ft()cossin td

∫

⋅

ub2

---U1t()

t()sin td

∫

⋅

---uc1 2

f0t

+()2

ft()sinsin td

∫

⋅

4PM

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

We get:

EQUATION C-49:

EQUATION C-50:

As Δf << f, from Equation C-49 and C-50, we have:

EQUATION C-51:

Therefore,

EQUATION C-52:

Assuming that the signal's initial phase angle measured in the 1st cycle is

1 and in

the N-th is

N, then the difference between actual frequency and the assumed

frequency is:

EQUATION C-53:

2uc1

-----------

f+()

()sin

πΔ

---------

⎝⎠

⎛⎞

sin

⋅⋅

f+()

⋅⋅

-------------------------------------------------------------------------

⋅

2uc1

-----------

()cos

πΔ

---------

⎝⎠

⎛⎞

sin

⋅⋅

f+()

⋅⋅

--------------------------------------------------------

⋅

-----

()sin

()cos

----------------------

≈

⎪

⎩

⎪

⎨

⎧

><+

<>+

≈

−

)0,0(,2)(

)0,0(,)(

)0,0(),(

)0,0(,

⎪

⎩

⎪

⎨

⎧

>−

⋅

⋅−−

−<−

⋅

⋅+−

<−

⋅

⋅−

≈Δ

)(,

)2(

)(,

)2(

)(,

)(

πϕϕ

ϕϕ

Error (%) m m r 7 Vollagi 7 Acme Puwer Peaclrve Power Currem 705 475 AB 485 49 495 5a 505 51 515 52 525 Frequency (HZ) @ 3 2Ksps

Power Calculation Theory

C.6 IMPROVING MEASUREMENT PRECISION OF QUASI-SYNCHRONOUS

SAMPLING ALGORITHM

When using the quasi-synchronous sampling method for harmonic analysis and

calculation of power as well as voltage and current, strict restrictions apply for the

algorithm and compensation, (i.e., the frequency offset must not exceed 1% of the

central frequency). Precision of the result increases as the frequency offset gets less.

Measurement accuracy is not guaranteed, if this condition can not be met. Figure C-4

shows the quasi-synchronization algorithm using 3 iterations with input signal ranging

from 47.5 Hz to 52.5 Hz. The algorithm is for calculating the active power, the reactive

power and the relative error of current and voltage. Figure C-4 shows that the algorithm

works well when the frequency falls in the range of 47.5 Hz to 52.5 Hz. As the

frequency deviates from the range, the error increases significantly. Therefore, the

algorithm needs to be improved to fit into more applications with a more relaxed

restriction.

FIGURE C-4: Quasi-sync Algorithm Error Analysis of 3 Iterations.

The quasi-sync sampling algorithm has relative high accuracy in frequency measure-

ment and the error can be less than 0.005 Hz. If the frequency range to be measured

can be segmented to make the frequency input closest to the multiple of cycle point,

and processed using appropriate quasi-sync window function and sine/cosine tale,

then the algorithm can be used for a much wider range of frequency .

Figure C-5 is the error analysis of the improved 3-iteration quasi-synchronous

algorithm at 3.2 ksps. It shows that the relative error for each result can be well

controlled when the frequency of the input signal falls in the range of 47.5 Hz to

52.5 Hz.

Figure C-5 clearly shows that the relative errors of the current, voltage, active power

and reactive power in the entire frequency range are less than 0.08%. Also, when the

input frequency is around the multiple of cycle frequencies (52.459 Hz, 51.613 Hz,

50.794 Hz, 50.0 Hz, 49.231 Hz, 48.485 Hz and 47.761 Hz), the calculateion error is

DUB nun \Ilun 2nd‘3vd harmonlc 20% W‘s“ 151 has: mama] 3p. D 07 Current _ Am: inev n 05 Reactwe Pow _ Frequency a o m DUB , Ermr m) 3 ZKSps 1: a b 002 - 001 D 475 43 435 49 495 5D 5u5 51 515 52 525 Fvequency (HZ) x m 15 ‘ ‘ ‘ ‘ ‘ ‘ ‘ Vnhage 5mm sandman 2nd31dhavmnmc=1ﬂ% “WWW" 15H] ase advancem 25 ‘ R’Eactwe inev F12 uen: m n y 7 D , ,5 ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘ 47 5 45 45 5 43 43 5 5m 5m 5 51 51 5 52 52 5 FvKuEnEy (HZ)

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

minimal (<0.01%). When the input frequency deviates from the multiple of cycle

frequencies, the calculation error increases rapidly. As the calculation error is related

to the frequency offset to the multiple of freqency point, the calculation error caused by

frequency offset can be corrected. Figure C-6 is the error analysis after frequency off-

set correction using simple parabolic interpolation. Calcultion errors for all parameters

are shown to be less than 0.015% after the correction.

FIGURE C-5: Error Analysis Of Improved Quasi-sync Calculation Using 3

Iterations.

FIGURE C-6: Calculation Error Analysis After The Frequency Offset

Compensation.

Power Calculation Theory

C.7 MEASURING SECONDARY PARAMETERS

The methods of measuring parameters such as RMS values of voltage and current,

active power, reactive power and frequency have been discussed in previous sections.

These are primary parameters that need to be calculated from the original data. There

are some other parameters called secondary parameter, such as power factor of each

phase, total reactive power, total active power, total power factor, harmonic

components and cumulative energy. They are obtained indirectly from primary param-

eters.

The measurement of secondary parameters is discussed in this section.

C.7.0.1 TOTAL ACTIVE POWER AND TOTAL REACTIVE POWER

For 3-phase 4-wire systems, 3-phase total active power and recative power are the

sum of power of each phase, respectively, which can be expressed as:

EQUATION C-54:

EQUATION C-55:

C.8 APPARENT POWER OF EACH PHASE AND TOTAL APPARENT POWER

Apparent power is defined as:

EQUATION C-56:

C.9 POWER FACTOR OF EACH PHASE AND TOTAL POWER FACTOR

Power factor is defined as the ratio of active power to apparent power. The definition

can be represented as shown in Equation C-57:

EQUATION C-57:

APBPC

++=

AQBQC

++=

2p2

PF P

P2Q2

------------------------=

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.10 Active Energy AND REACTIVE ENERGY

Active energy is defined as the integral of active power over time, which is:

EQUATION C-58:

In this design, active energy is obtained from multiplying the voltage by the current

sampled each time. The phase angle difference is compensated after each power

measurement is completed.

For reactive power, the cumulative reactive energy over a time period can be calculated

by measuring the average power and calculating the time interval between 2 measure-

ments.

EQUATION C-59:

C.11 POSITIVE/NEGATIVE ACTIVE ENERGY, POSITIVE/NEGATIVE REACTIVE

ENERGY AND FOUR-QUADRANT REACTIVE ENERGY

In the measurement plane, the horizontal axis denotes voltage vector U (fixed on the

horizontal axis). The instantaneous current vector is used to represent the power

transfer, and has a phase angle φ against vector U. φ is positive in counter-clockwise

direction. Power exchange can be defined in 4 scenarios:

• Quadrant I (P>0, Q>0): active energy and reactive energy are sent out at the

same time;

• Quadrant II (P<0, Q>0): active energy is sent in while reactive energy is sent out;

• Quadrant III (P<0, Q<0): active energy is sent in while reactive energy is

absorbed;

• Quadrant IV (P>0, Q<0): active energy is sent out while the reactive energy is

absorbed.

1. Positive active energy and negative active energy: accumulated active

energy can be defined as positive and negative depending on the direction of

active current. When the direction of active current is positive (from power grid to

loads), active energy is positive (where active power P>0, corresponding to

quadrants I and IV, which means that loads are drawing energy from grid). When

current moves from loads to power grid, it is defined as negative active energy

(where active power P < 0, corresponding to quadrants II and III, which means

energy is provided to grid). Usually only positive active energy is taken into

account in active energy, but in practice negative active energy may be taken into

account as well, if necessary.

2. Positive reactive energy and negative reactive energy: If reactive power

Q > 0 (corresponding to quadrants I and II), it means power grid is providing

reactive energy to loads, so the energy is defined as positive reactive energy.

When reactive power Q < 0 (corresponding to quadrants III and IV), it means

that loads are providing reactive energy to power grid, so the energy is defined

as negative reactive energy.

WPt() td

∫uk() ik()

⋅⋅

k0=

∑

VrQ

∫t()dt=

w «at;

Power Calculation Theory

3. Four-quadrant reactive energy: metering reactive energy in positive/negative

reactive energy cannot truly reflect the status of reactive energy, whereas

4-quandrant reactive energy measuring gives a true picture of energy exchange.

Reactive energy in four quadrants represents four different reactive energy (see

Figure C-7). And the reactive energy is accumulated depending on which

quadrant it is located.

FIGURE C-7: Definition Of 4 Quadrants To Measure Electrical Energy.

图2.4 电能测量四象限定义

Active in (+A)

I (RL)

II (RC)

III (-RL)IV (-RC)

Reactive in (+R)

Reactive out (-R)

Active out (-A)

A－有功电能；R—无功电能；RL—感性无功电能；RC—容性无功电能

电流向量

电压向量

图2.4 电能测量四象限定义

Active in (+A)

I (RL)

II (RC)

III (-RL)IV (-RC)

Reactive in (+R)

Reactive out (-R)

Active out (-A)

A－有功电能；R—无功电能；RL—感性无功电能；RC—容性无功电能

电流向量

电压向量

Active in (+A)

I (RL)

II (RC)

III (-RL)IV (-RC)

Reactive in (+R)

Reactive out (-R)

Active out (-A)

A－有功电能；R—无功电能；RL—感性无功电能；RC—容性无功电能

Active in (+A)

I (RL)

II (RC)

III (-RL)IV (-RC)

Reactive in (+R)

Reactive out (-R)

Active out (-A)

A－有功电能；R—无功电能；RL—感性无功电能；RC—容性无功电能

电流向量

电压向量

Voltage vector

Current vector

Where:

A=is active energy,

R=is reactive energy

RL=is inductive reactive energy

RC=s capacitive reactive energy

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.12 HARMONIC COMPONENTS OF CURRENT, VOLTAGE AND TOTAL

HARMONIC DISTORTION

In Section C.3 “The Harmonic Analysis Algorithm Of Quasi-synchronous Sam-

pling”, we discussed the measuring of current and voltage signals for each order of

harmonics. 3 parameters are used to show to what extent a distorted wave deviates

from a sine wave. They are: harmonic content, total distortion and harmonic ratio of the

k-th harmonic. The term harmonic content means the root of square of effective values

for all harmonics, which is defined as:

EQUATION C-60:

The total voltage distortion ratio of harmonics is the ratio of harmonic content to the

fundamental in percentage, which is defined as:

EQUATION C-61:

The k-th harmonic ratio for voltage is the ratio of the k-th harmonic to the fundamental

in percentage, defined as:

EQUATION C-62:

Similarly, harmonics of each order for the current and total distortion ratio can be sorted

out.

UHUk2

k2=

∑

THDU

------- 100%

THDUk

()

k2=

∑

THDUk

------ 100%

Power Calculation Theory

C.13 COMPENSATION FOR RATIO ERROR AND PHASE LAG

The error of the current transformer (CT) is a complex, which can usually be expressed

by two orthogonal parts, current error (f) and phase lag (δ).

EQUATION C-63:

The current error, also known as ratio error, can be written in percentage as:

EQUATION C-64:

Phase lag, also known as angle error, is the phase difference between primary and

secondary current vector, in 'minute'.

Different current transformers have different errors. Current transformers are classified

into different accuracy classes depending on their error magnitudes. The accuracy

class of a transformer is nominated by the percentage of the maximal ratio error

allowed for a given rated current.

Accuracy classes and corresponding error limits for a current transformer are listed in

Table C-1.

TABLE C-1: ACCURACY CLASS AND ERROR LIMIT FOR THE CURRENT TRANSFORMER

δ⋅

f 100 knI2I1

–()

-------------------------

Where:

Kn=the rated current ratio

I1=the primary current

I2=the secondary current that passes I1

under the test condition

Accurate

Class

Ratio Error± (%) Phase lag

Rated Current (%) ± (%) ± (Grad)

Rated Current (%) Rated Current (%)

1 5 20 100 120 1 5 20 100 120 1 5 20 100 120

0.1 0.4 0.2 0.1 0.1 15 8 5 5 0.45 0.24 0.15 0.15

0.2 0.75 0.35 0.2 0.2 30 15 10 10 0.9 0.45 0.3 0.3

0.5 1.5 0.75 0.5 0.5 90 45 30 30 2.7 1.35 0.9 0.9

13 1.5 1.0 1.0 180 90 60 60 5.4 2.7 1.8 1.8

Rated Current (%) Phase difference

50 120

333 Phase difference of class 3 and class 5 are not specified.

555

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.14 RELATIONSHIP BETWEEN ERROR AND CURRENT

For a given load and frequency, the absolute ratio error and angle error increase when

the primary current decreases from the rated value for un-compensated current trans-

former. The reason is that with the decrease of the secondary current, the magnetic

permeability µ of the iron core varies non-linearly, resulting in less reduction in the field

ampere turns.

Figure C-8 is a typical curve for load current and the phase lag of a CT. Generally,

phase lag of the output signal is great when the load current is small, and also

increases at a fast rate.

FIGURE C-8: Current Load Versus CT Phase Lag.

Current Load

Phase Lag

Inpm Voltage Inpm Current CT 2000:1

Power Calculation Theory

C.15 RATIO ERROR COMPENSATION

As non-linearity and inconsistency exist in the sampling circuit (including CT and

back-end shunt resistors) and the ADC circuit, it is necessary to compensate for ratio

error to the system. Figure C-9 is the transfer link of the voltage and current channels.

The compensation for ratio error is quite simple. It compares the measured value

against the actual input value under certain input conditions and obtains a correction

coefficient.

EQUATION C-65:

FIGURE C-9: Error Caused By Sampling Circuit And ADC.

Since current has a large dynamic range, for a meter which requires high accuracy

(0.2s and 0.5s), the multi-point calibration method is needed to meet input requirement

for full range. The MCP3909 device's current channel includes an adjustable gain

amplifier. The ratio error must be recalibrated for different amplification, but only needs

to be calibrated once under the same amplification conditions.

Correction coefficient Coefficient before correction Calibration Value

Measured Value

-------------------------------------------

Input

Voltage

R0 CT

1:1 ADC

R0 R0

Voltage primary

Sampling resistor

Voltage secondary

Sampling resistor

Input

Current

2000:1 ADC

R2 R2

Current secondary

Sampling resistor

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

C.16 PHASE LAG COMPENSATION

Phase lag of a CT has no effect on the metering of RMS current/voltage and apparent

power, but will affect the metering of power, since the phase lag will change the phase

relationship between the input current and the voltage. This will result in a deviation of

the calculated active power from the calculated reactive power.

Figure C-10 shows how a transformer's phase lag affects the measured results under

both inductive and capacitive loads. Let's assume that the output of CT has no phase

lag from the input voltage, while the CT has a phase lag from the input signal. With

inductive loads, the phase angle increases between the volatge and the current

because of the phase lag induced by the CT, resulting in a decrease of the measured

active power and an increase of the reactive power. While with capacitive loads, the

phase angle between the voltage and the current decreases because of the phase lag

induced by the CT, resulting in a decrease of the measured reactive power and an

increase of active power.

There are many methods for phase lag compensation. In this design the result correc-

tion method is used. It compensates with a coefficient after the active power and

reactive power are figured out, which has a small amount of calculation.

FIGURE C-10: Measurement Change Caused By Transformer Phase Lag.

Assuming that the phase lag of CT is ϕi, of PT is ϕu, after PT and CT, the variation of

phase lag between current and voltage is:

Δϕ

u–

FIGURE C-11: Principle Of Phase Lag Correction.

Input

current

CT Output

current

Input

voltage

Capacitive

Load

Inductive

Load

Δθ

Input

current

CT Output

current

Input

voltage

Capacitive

Load

Inductive

Load

Δθ

Δf

Power Calculation Theory

Given that the phase lag between the input voltage and current is φ, after PT and CT,

the actual measured active power is P', reactive power is Q'. RMS current is I, RMS

voltage is V, input apparent power is S, actual input active power is P and reactive

power is Q, then Figure C-11 can be drawn based on the principles of power triangle.

EQUATION C-66:

EQUATION C-67:

From the above 2 equations, we have:

EQUATION C-68:

EQUATION C-69:

Where:

EQUATION C-70:

EQUATION C-71:

By setting up certain input conditions, Δϕ can be measured, and then k1 and k2 can be

calculated.

In this design, we use an input of 0.5L for calibration. With this condition, Δϕ can be

calculated using the difference between the meaured and the actual input value of

active power. For accurate calculations, the user may also use the difference between

the measured cumulative energy and the actual cumulative energy to calculate the

difference.

EQUATION C-72:

Where err is the error rate of the energy measurement, which results from calculating

the error between the actual energy measured by a standard meter and the energy

measured by the dsPIC devices. The error can be obtained from the output of the meter

calibration workbench.

EQUATION C-73:

P'VI

φΔϕ

+()cos

⋅⋅

Δϕ

cos Q

Δϕ

sin–==

Q'VI

φΔϕ

+()sin

⋅⋅

Δϕ

cos P

Δϕ

sin–==

1P'k2Q'+=

1Q'k2P'–=

Δϕ

cos=

sin

Δϕ

aP'

⋅

-----------

⎝⎠

⎛⎞

---

–cos a 0.5 1 err+()

⋅

()

---

–

⎝⎠

⎛⎞

cos==

err P'P–

--------------

------- 100

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

Since the phase lag of a CT's output signal is related to the magnitude of current,

different correction coefficients, K, can be set according to different RMS current

values. In this design, 5 calibration points can be set. If it does not require high-preci-

sion, fewer points can be set to simplify calibration.

If one-time calibration cannot meet the precision requirement, more calibrations can be

done. The new angle error may still be calculated using Equation C-72. The new

correction coefficient is:

EQUATION C-74:

EQUATION C-75:

C.16.0.1 PHASE LAG COMPENSATION WHEN FREQUENCY VARIES

For the same current intensity, the signal delay caused by the CT is the same. When

the frequency of the input signal varies, the phase lag will be different. Normally,

calibration is done at 50 Hz. When the frequency varies, if the same phase lag

compensation coefficient for 50 Hz is still used, it will cause an error in the power

measurement. In most cases, the frequency varies in a small range (test specification

requires ±2.5%), so it has little effect on the measurement accuracy. For meters with

an accuracy of 0.5s or above, this measurement error can be ignored. But for 0.2s

meters, the error cannot be ignored and the frequency variation needs to be corrected

during calculation.

The phase lag compensation coefficient k1 and k2 are corrected during calculation.

Assuming that the freqnency is 50 Hz, the signal delay caused by CT is t, then after

correction, the compensation coefficient k1 and k2 will be:

EQUATION C-76:

EQUATION C-77:

When frequency varies, assuming that the frequency offset is Δf, i.e. the input signal

frequency is 50 + Δf, then the compensation coefficient will be:

EQUATION C-78:

EQUATION C-79:

k'1

Δϕ

+()cos k1

Δϕ

cos k2

Δϕ

sin

⋅

–

⋅

k'2

Δϕ

+()sin k2

Δϕ

cos k1

Δϕ

sin

⋅

–

⋅

Δϕ

cos t 50 2

π⋅⋅

()cos==

sin

t502

π⋅⋅

()sin==

k'1

Δϕ

cos t 50

f+()2

π⋅⋅

()cos==

k'2

sin

t50

f+()2

π⋅⋅

()sin==

Power Calculation Theory

To avoid complexity in calculation and to maximize the correction precision, the

following equations may be used to approximate K1 and K2 when the phase angle is

small.

EQUATION C-80:

EQUATION C-81:

k'1

Δϕ

cos

Δϕ

cos

------sin2

Δϕ⋅

–

≈

------k2k2

⋅⋅

–=

k'2

sin

ϕΔ

sin

ϕΔ

------sin

Δϕ Δϕ

cos

⋅⋅

–

≈

------k1k2

⋅⋅

–=

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design

NOTES:

6‘ MICROCHIP

MCP3909 / DSPIC33F 3-PHASE

ENERGY METER REFERENCE DESIGN

Appendix D. 50/60 Hz Meter Operation

D.1 FIRMWARE VERSIONS

There are two versions of firmware for the meter due to the quasi-synchronous

sampling scheme employed by the dsPIC33F firmware. The design covers the

frequency of rated frequency ±2.5 Hz.

To change the rated frequency, just change the definition in the beginning of

cacul.h - #define STD_FREQ 50.0.

This is provided for download from Microchip’s website, file names and checksums

below.

At the same time you need to change the crystal to provide clock for metering IC.

TABLE D-1: FIRMWARE FILES

Line Frequency Firmware Name Hex File Checksum YXX VALUE

50 Hz PM_1_50.ZIP TBD 3.857 MHz

60 Hz PM_1_60.ZIP TBD TBD

Q ‘MICROCHIP

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