ADE7754 datasheet(28/44 Pages) AD

28 / 44 page

REV. PrG 01/03

PRELIMINARY TECHNICAL DATA

ADE7754

– 28 –

The total apparent power calculated by the ADE7754 de-

pends on the configuration of the VAMOD bits in the

VAMode register. Each term of the formula can be disabled

or enabled by the setting VASEL bits respectively to logic 0

or logic 1 in the VAMode register. The different configura-

tions are described in Table IV.

VA-

VASEL0

VASEL1

VASEL2

MOD

VArms x IArms

+ VBrms x IBrms

+ VCrms x ICrms

VArmsxIArms

+(VArms+VCrms)/2xIBrms+ VCrms x ICrms

VArms x IArms

+ VArms x IBrms

+ VCrms x ICrms

Table IV -Total Apparent Power calculation

Note: VArms, VBrms, VCrms, IArms, IBrms and ICrms represent

respectively the voltage and current channels RMS values of

the corresponding registers.

For example, for VAMOD = 1, the exact formula that is used

to process the Apparent Power is:

Total Apparent Power

AVAG

Arms

Crms

=⋅

⋅ +









(()

⋅⋅ +









+⋅

⋅ +









BVAG

CVAG

Brms

Crms

Depending on the polyphase meter configuration, the appro-

priate formula should be chosen to calculate the Apparent

Energy. The American ANSI C12.10 standard defines the

different configurations of the meter. Table V describes

which mode should be chosen in these different configura-

tions.

ANSI Meter Form

VAMOD

VASEL

5S/13S

3-wire Delta

3 or 5 or 6

6S/14S

4-wire Wye

8S/15S

4-wire Delta

9S/16S

4-wire Wye

Table V - Meter form configuration

Different gain calibration parameters are offered in the

ADE7754 to cover the calibration of the meter in different

configurations. These registers, APGAIN, VGAIN and

VAGAIN, have different purposes in the signal processing of

the ADE7754.

APGAIN registers affect the Apparent power calculation but

should be used only for Active Power calibration. VAGAIN

registers are used to calibrate the Apparent Power calcula-

tion.

VGAIN registers have the same effect as VAGAIN registers

when VAMOD=0 or 2. They

should be left at their default

value in these modes. VGAIN registers should be used to

compensate

gain

mismatches

between

channels

VAMOD=1.

As mentioned before, the offset compensation of the Phase

Apparent Power calculation is done in each individual RMS

measurement signal processing -see Apparent Power Offset com-

pensation.

APPARENT ENERGY CALCULATION

The Apparent Energy is given as the integral of the Apparent

Power.

Apparent Energy

Apparent Power t dt

∫

()

(21)

The ADE7754 achieves the integration of the Apparent

Power signal by continuously accumulating the Apparent

Power signal in an internal non-readable 49-bit register. The

Apparent Energy register (VAENERGY[23:0]) represents

the upper 24 bits of this internal register. This discrete time

accumulation or summation is equivalent to integration in

continuous time. Equation 22 below expresses the relation-

ship

Apparent Energy

Lim

Apparent Power nT

=×













→

∞

∑

()

(22)

Where n is the discrete time sample number and T is the

sample period.

The discrete time sample period (T) for the accumulation

Figure 35 shows a graphical representation of this discrete

time integration or accumulation. The Apparent Power

signal is continuously added to the internal register. This

addition is a signed addition even if the Apparent Energy

remains theoretically always positive.

TOTAL APPARENT POWER

00000h

D1B71h

time (nT)

TOTAL APPARENT POWER ARE

ACCUMULATED (INTEGRATED) IN

THE APPARENT ENERGY REGISTER

Apparent Power

Signal - P

VAENERGY[23:0]

VADIV

Figure 35-ADE7754 Apparent Energy calculation

The upper 49-bit of the internal register are divided by

VADIV. If the value in the VADIV register is equal to 0 then

the internal active Energy register is divided by 1. VADIV is

an 8-bit unsigned register. The upper 24-bit are then written

in the 24-bit Apparent Energy register (VAENERGY[23:0]).

RVAENERGY register (24 bits long) is provided to read the

Apparent Energy. This register is reset to zero after a read

operation.

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