ADE7754 datasheet(27/44 Pages) AD

27 / 44 page

REV. PrG 01/03

PRELIMINARY TECHNICAL DATA

ADE7754

– 27 –

00000h

D1B71h

+ 100% FS

- 100% FS

F2E48Fh

+ 150% FS

+ 50% FS

- 50% FS

- 150% FS

13A929h

68DB9h

F97247h

EC56D7h

AVAGAIN[11:0]

000h 7FFh 800h

Apparent Power

Voltage channel and Current channel 0.5V / GAIN

Figure 33 - Apparent Power Calculation Output range

Apparent Power Offset Calibration

Each RMS measurement includes an offset compensation

RMS value -see Current RMS calculation and Voltage RMS

calculation. The Voltage and Current RMS values are then

multiplied together in the Apparent Power signal processing.

As no additional offsets are created in the multiplication of

the RMS values, there is no specific offset compensation in

the Apparent Power signal processing. The offset compensa-

tion of the Apparent Power measurement in each phase is

done by calibrating each individual RMS measurements.

TOTAL APPARENT POWER CALCULATION

The sum of the Apparent powers coming from each phase

gives the total Apparent Power consumption. Different com-

binations of the three phases can be selected in the sum by

setting bits 7-6 of the VAMode register (mnemonic

VAMOD[1:0]). Figure 34 demonstrates the calculation of

the total apparent power.

PHASE A*

Total Apparent

Power Signal

PHASE B*

PHASE C*

RMS

AAPGAIN

AVAGAIN

RMS

AVGAIN

RMS

BAPGAIN

BVAGAIN

RMS

BVGAIN

RMS

CAPGAIN

CVAGAIN

RMS

CVGAIN

Arms

Crms

Arms

Crms

Figure 34-Total Apparent Power calculation

APPARENT POWER CALCULATION

Apparent power is defined as the maximum active power that

can be delivered to a load. As Vrms and Irms are the effective

voltage and current delivered to the load, the Apparent Power

(AP) is defined as Vrms x Irms.

Note that the Apparent power is equal to the multiplication

of the RMS values of the voltage and current inputs. For a

poly-phase system, the RMS values of the current and voltage

inputs of each phase (A, B and C) are multiplied together to

obtain the apparent power information of each phase. The

total apparent power is the sum of the apparent powers of all

the phases. The different solutions available to process the

total apparent power are discussed in the following para-

graph.

Figure 32 illustrates graphically the signal processing in each

phase for the calculation of the Apparent Power in the

ADE7754.

0.5V / GAIN2

0.5V / GAIN1

Current RMS Signal - i(t)

Voltage RMS Signal - v(t)

MULTIPLIER

Apparent Power

Signal - P

Irms

Vrms

00h

D1B71h

AVAG

1CF68Ch

Figure 32 - Apparent Power Signal Processing

The Apparent Power is calculated with the Current and

Voltage RMS values obtained in the RMS blocks of the

ADE7754. Shown in Figure 33 is the maximum code

(Hexadecimal) output range of the Apparent Power signal for

each phase. Note that the output range changes depending on

the contents of the Apparent Power Gain registers but also on

the contents of the Active Power Gain and Voltage Gain

registers – see Current RMS calculation and Voltage RMS

calculation. Only the effect of the Apparent Power Gain is

shown on Figure 33. The minimum output range is given

when the Apparent Power Gain register content is equal to

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

Apparent Power Gain register. This can be used to calibrate

the Apparent Power (or Energy) calculation in the ADE7754

for each phase and also the Total Apparent Energy -see Total

Apparent Power calculation.

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