ADE7754_15 datasheet(18/44 Pages) AD

18 / 44 page

REV. 0

–18–

ADE7754

Figure 24 shows the signal processing in each phase for the

active power in the ADE7754.

Figure 25 shows the maximum code (hexadecimal) output

range of the active power signal (after AWG). Note that the

output range changes depending on the contents of the active

power gain and watt gain registers. See the Current Channel

ADC section. The minimum output range is given when the

active power gain and watt gain registers contents are equal to

800h, and the maximum range is given by writing 7FFh to the

active power gain and watt gain registers. These can be used to

calibrate the active power (or energy) calculation in the

ADE7754 for each phase and the total active energy. See the

Total Active Power Calculation section.

0000000h

D1B717h

+ 100% F5

– 100% FS

2E48E9h

+ 150% FS

+ 50% FS

– 50% FS

– 150% FS

13A92A4h

68DB8Ch

972474h

EC56D5Ch

AAPGAIN[11:0] OR AWGAIN[11:0]

000h

7FFh

800h

ACTIVE

POWER

CURRENT CHANNEL

0.5V/GAIN1

VOLTAGE CHANNEL

0.5V/GAIN2

Figure 25. Active Power Calculation Output Range

Power Offset Calibration

The ADE7754 also incorporates an active offset register on each

phase (AAPOS, BAPOS, and CAPOS). These are signed twos

complement 12-bit registers that can be used to remove offsets

in the active power calculations. An offset may exist in the

power calculation because of crosstalk between channels on the

PCB or in the IC itself. The offset calibration allows the con-

tents of the active power register to be maintained at zero when

no power is being consumed.

One LSB in the active power offset register is equivalent to one

LSB in the 28-bit energy bus displayed in Figure 24. Each

time power is added to the internal active energy register, the

content of the active power offset register is added. See the

Total Active Power Calculation section. Assuming the average

value from LPF2 is 8637BCh (8,796,092d) with full ac scale

inputs on current channel and voltage channel, then one LSB in

the LPF2 output is equivalent to 0.011% of measurement error

at –60 dB down of full scale. See the Calibration of a 3-Phase

Meter Based on the ADE7754 Application Note AN-624.

CURRENT SIGNAL – i(t)

–100% TO +100% FS

VOLTAGE SIGNAL – v(t)

–100% TO + 100% FS

INSTANTANEOUS

POWER SIGNAL – p(t)

MULTIPLIER

ACTIVE POWER

SIGNAL – P

28F5h

D70Bh

28F5C2h

D70A3Eh

00h

AWG

D1B717h

1V/GAIN1

1V/GAIN2

HPF

LPF2

SGN

210

APOS[11:0]

SGN

Figure 24. Active Power Signal Processing

Reverse Power Information

The ADE7754 detects when the current and voltage channels

of any of the three phase inputs have a phase difference greater

than 90

° (i.e., |

A| or |

B| or |

C| > 90

°). This mechanism

can detect wrong connection of the meter or generation of

active energy.

The reverse power information is available for Phase A, Phase B,

and Phase C, respectively, by reading Bits 12 to 14 of the CFNUM

sign of the active power of the corresponding phase. Logic 1

corresponds to negative active power.

The AENERGY phase selection bits (WATSEL bits of the

WATMode register) enable the negative power detection per

phase. If Phase A is enabled in the AENERGY accumulation,

Bit 5 of WATMode register sets to Logic 1 and the negative

power detection for Phase A—Bit 12 of CFNUM register—

indicates the direction of the active energy. If Phase A is

disabled in the AENERGY register, the negative power bit for

Phase A is set to Logic 0.

TOTAL ACTIVE POWER CALCULATION

The sum of the active powers coming from each phase provides

the total active power consumption. Different combinations of

the three phases can be selected in the sum by setting Bits 7 and

6 of the WATMode register (mnemonic WATMOD[1:0]).

Figure 26 demonstrates the calculation of the total active power,

which depends on the configuration of the WATMOD bits in

the WATMode register. Each term of the formula can be disabled

or enabled by setting WATSEL bits respectively to Logic 0 or

Logic 1 in the WATMode register. The different configurations

are described in Table I.

Table I. Total Active Power Calculation

WATMOD WATSEL0

WATSEL1

WATSEL2

IA*

+ VB

IB*

+ VC

IC*

(IA*–IB*)+ 0

+ VC

(IC*–IB*)

(IA*–IB*)+ 0

+ VC

IC*

Note that IA*, IB*, and IC* represent the current channel

samples after APGAIN correction and high-pass filtering.

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