AT73C500 데이터 시트보기 (PDF) - Atmel Corporation

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AT73C500

Chip Set Solution for Watt-Hour Meters

Atmel Corporation 

AT73C500

Measurements and Calculations

The first operation performed by AT73C500 is digital high-

pass filtering. The purpose of the filtering is to remove the

DC offset of both current and voltage samples.

From offset free samples, active power is calculated

phase-by-phase with simple multiplication and addition

operations.

First, the current samples are multiplied by voltage sam-

ples. The multiplication results are summed over one line

period and finally the sum value is divided by 64. This dis-

crete time operation gives the average power of one

50/60Hz period and the result corresponds to the following

continuous time formula:

N T



∑ ∫ P =







T-1--

×



[AN

×

UN

×

sin { n

×

wt }

×

AN

×

IN

×

sin { n

×

wt

+

∅N}

dt ]



n = 0 0



N

∑ =





12--

×

An

×

An

×

Un

×

In

×

cos ( ∅n )

n=0

where

T = 1/50 Hz or 1/60 Hz,

n = 1, 2, 3,..., 20 (basic 50/60 Hz frequency and the

harmonics),

An = frequency response of calculations.

The total power is calculated by summing the power of

each line phase. Reactive power calculation is based on a

similar procedure. Before multiplying the current and volt-

age samples AT73C500 performs a frequency independent

-90 degree phase shift of the voltage signal. This is realized

with a digital Hilbert transformation filter. The bandwidth of

reactive power measurement is limited to 360 Hz.

Based on the active and reactive results apparent power

and power factors are determined. RMS phase voltages

are calculated by squaring and summing the voltage sam-

ples and finally taking a square root of the results. Current

is determined by dividing apparent power result by corre-

sponding phase voltage.

Frequency measurement is based on a comparison of the

line frequency and AT73C500 sampling clock frequency.

The measurement range is from 20 Hz to 350 Hz.

All measurements and calculations, except frequency mea-

surement, are made over 10 line cycle periods. The results

are updated and transferred to processor bus once in 200

ms.

Measurement Registers

For the measurement parameters 25 registers are allo-

cated:

Register

REG0

REG1

REG2

REG3

REG4

REG5

REG6

REG7

REG8

REG9

REG10

REG11

REG12

REG13

REG14

REG15

REG16

REG17

REG18

REG19

REG20

REG21

REG22

REG23

REG24

Meaning

Phase 1, active power, P1(10T), 32-bit register;

Phase 2, active power, P2(10T), 32-bit register;

Phase 3, active power, P3(10T), 32-bit register;

Phase 1, reactive power, Q1(10T), 32-bit register;

Phase 2, reactive power, Q2(10T), 32-bit register;

Phase 3, reactive power, Q3(10T), 32-bit register;

Phase 1, apparent power, S1(10T), 16-bit register;

Phase 2, apparent power, S2(10T), 16-bit register;

Phase 3, apparent power, S3(10T), 16-bit register;

Phase 1, power factor, PF1, 16-bit register;

Phase 2, power factor, PF2, 16-bit register;

Phase 3, power factor, PF3, 16-bit register;

Active exported energy since the latest reset, +Wp,

32-bit counter;

Active imported energy since the latest reset, -Wp,

32-bit counter;

Reactive energy, inductive load, Wqind, 32-bit

counter;

Reactive energy, capacitive load, Wqcap, 32-bit

counter;

Number of 10T periods elapsed since the latest

reset, 32-bit counter;

Frequency, f, 16-bit register;

Reserved for further use, 16-bit register;

Phase 1, voltage U1, 16-bit register;

Phase 2, voltage U2, 16-bit register;

Phase 3, voltage U3, 16-bit register;

Phase 1, current I1, 16-bit register;

Phase 2, current I2, 16-bit register;

Phase 3, current I3, 16-bit register.

The size of the registers is either 16-bit or 32-bit. IEC spec-

ifications apply to the calculations of active and reactive

power and energy (REG 0-5 and REG 12-15). Other results

are intended mainly for demand recording and for various

diagnostic and display functions. The accuracy of those are

limited due to the finite resolution.

9

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