ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 50

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

ADE7880
Because V rms and I rms contain all harmonic information, the
apparent power computed by the ADE7880 is total apparent
power. The ADE7880 computes fundamental and harmonic
apparent powers determined by the fundamental and harmonic
components of the voltages and currents. Please see Harmonics
calculations section for details.
The ADE7880 stores the instantaneous phase apparent powers
into the AVA, BVA, and CVA registers. Their expression is
where:
U, I are the rms values of the phase voltage and current.
Apparent Power Gain Calibration
The average apparent power result in each phase can be scaled
by ±100% by writing to one of the phase’s PGAIN 24-bit
registers (APGAIN, BPGAIN, or CPG AIN). Note that these
registers are the same gain registers used to compensate the
other powers computed by the ADE7880. Please see Active
Power Gain Calibration section for details on these registers.
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 Root Mean Square Measurement section). The voltage
and current rms values are 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
compensation of the apparent power measurement in each phase is
accomplished by calibrating each individual rms measurement.
Apparent Power Calculation Using VNOM
The ADE7880 can compute the apparent power by multiplying
the phase rms current by an rms voltage introduced externally in
the VNOM 24-bit signed register.
xVA
AVRMS
AIRMS
=
Digital Signal Processor
U
U
FS
×
I
I
FS
×
PMAX
APGAIN
×
2
1
4
Figure 54. Apparent Power Data Flow and Apparent Energy Accumulation
2
:
4
AVA
Rev. PrE | Page 50 of 103
(40)
Σ
34
VATHR
THRESHOLD
U
the ADC inputs are at full scale.
PMAX =27,059,678, the instantaneous power computed when
the ADC inputs are at full scale and in phase.
The xVA[23:0] waveform registers may be accessed using
various serial ports. Refer to the Waveform Sampling Mode
section for more details.
The ADE7880 can compute the apparent power in an alternative
way by multiplying the phase rms current by an rms voltage
introduced externally. See the Apparent Power Calculation
Using VNOM section for details.
When one of Bits[13:11] (VNOMCEN, VNOMBEN, or
VNOMAEN) in the COMPMODE register is set to 1, the
apparent power in the corresponding phase (Phase x for
VNOMxEN) is computed in this way. When the VNOMxEN
bits are cleared to 0, the default value, then the arithmetic
apparent power is computed.
The VNOM register contains a number determined by U, the
desired rms voltage, and
tage when the ADC inputs are at full scale:
where U is the nominal phase rms voltage.
As stated in the Current Waveform Gain Registers, the serial
ports of the ADE7880 work on 32-, 16-, or 8-bit words. Similar
to the register presented in Figure 32, the VNOM 24-bit signed
register is accessed as a 32-bit register with the eight MSBs
padded with 0s.
Apparent Energy Calculation
Apparent energy is defined as the integral of apparent power.
27
Accumulator
FS
, I
Internal
26
Apparent Energy = ∫s(t)dt
VNOM
FS
are the rms values of the phase voltage and current when
0
=
U
0
U
FS
Preliminary Technical Data
×
, 3
766
U
FS
,
572
, the rms value of the phase vol-
Σ
32 bit register
AVAHR[31:0]
(41)
(42)