Datasheet

REV. 0
ADE7754
–25–
and voltage gain registers. See the Current RMS Calculation
and Voltage RMS Calculation sections. Only the effect of the
apparent power gain is shown on Figure 35. 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 the total apparent energy.
See the Total Apparent Power Calculation section.
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 35. Apparent Power Calculation Output Range
Apparent Power Offset Calibration
Each rms measurement includes an offset compensation register
to calibrate and eliminate the dc component in the rms value.
See the Current RMS Calculation and Voltage RMS Calculation
sections. The voltage and current rms values are then multiplied
in the apparent power signal processing. Because 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 compensation of the apparent power
measurement in each phase is done by calibrating each indi-
vidual rms measurement.
TOTAL APPARENT POWER CALCULATION
The sum of the apparent powers coming from each phase gives
the total apparent power consumption. Different combinations
of the three phases can be selected in the sum by setting Bits 7
and 6 of the VAMode register (mnemonic VAMOD[1:0]). Figure 36
demonstrates the calculation of the total apparent power.
I
A
V
A
24
RMS
AAPGAIN
RMS
AVAGAIN
V
ARMS
AVGAIN
PHASE A
I
C
V
C
24
RMS
CAPGAIN
RMS
CVAGAIN
V
CRMS
CVGAIN
PHASE C
I
B
V
B
24
RMS
BAPGAIN
RMS
BVAGAIN
BVGAIN
PHASE B
%
V
ARMS
2
+
V
CRMS
+
TOTAL APPARENT
POWER SIGNAL
Figure 36. Total Apparent Power Calculation
The total apparent power calculated by the ADE7754 depends on
the configuration of the VAMOD bits in the VAMode register.
Each term of the formula used can be disabled or enabled by the
setting VASEL bits, respectively, to Logic 0 or Logic 1 in the
VAMod
e register. The different configurations are described in
Table IV.
Table IV. Total Apparent Power Calculation
VAMOD VASEL0 VASEL1 VASEL2
0d V
ARMS
× I
ARM S
+ V
BRMS
× I
BRM S
+ V
CRMS
× I
CRMS
1d V
ARMS
× I
ARM S
+(V
ARMS
+ V
CRMS
)
/
2  I
BRM S
+ V
CRMS
× I
CRMS
2d V
ARMS
× I
ARM S
+ V
ARMS
× I
BRM S
+ V
CRMS
× I
CRMS
Note that V
ARMS
, V
BRMS
, V
CRMS
, I
ARMS
, I
BRMS
, and I
CRMS
represent
the voltage and current channels RMS values of the corresponding
registers.
For example, for VAMOD = 1, the formula used to process the
apparent power is
Total Apparent Power V I
AVAG
VV
I
BVAG
VI
CVAG
ARMS ARMS
ARMS CRMS
BRMS
CRMS CRMS
=××+






+
+
××+






+××+






1
2
2
1
2
1
2
12
12
12
()
The polyphase meter configuration determines which formula
should be used 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 for
different configurations.
Table V. Meter Form Configuration
ANSI Meter Form VAMOD VASEL
5S/13S 3-wire Delta 0 3 or 5 or 6
6S/14S 4-wire Wye 1 7
8S/15S 4-wire Delta 2 7
9S/16S 4-wire Wye 0 7
Different gain calibration parameters are offered in the ADE7754
to cover the calibration of the meter in different configurations.
The APGAIN, VGAIN, and VAGAIN registers 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 calculation. VGAIN regis-
ters 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 in VAMOD = 1.
As mentioned previously, the offset compensation of the phase
apparent power calculation is done in each individual rms mea-
surement signal processing. See the Apparent Power Offset
Calibration section.