UG-1098
ADE9000 Technical Reference Manual
Rev. 0 | Page 14 of 86
Neutral Current RMS, Vector Current Sum
The
calculates the neutral current rms from a neutral
current sensor input into the INP and INN pins, and stores the
result in the NIRMS register. A NIRMSOS register allows offset
calibration of this measurement. The scaling is the same as for
the other xIRMS and xIRMSOS registers (see the Filter-Based
Total RMS section for more information).
The
also calculates the rms of the sum of
IA + IB + IC ± IN and stores the result in the ISUMRMS register.
The ISUMRMSOS register allows offset calibration of this
measurement. The scaling is the same as for the other xIRMS
and xIRMSOS registers (see the Filter-Based Total RMS section
for more information).
If a neutral current sensor is not used, write the
ISUM_CFG[1:0] bits in the CONFIG0 register equal to 0, and
then ISUMRMS approximates the neutral current from the sum
of IA, IB, and IC.
If the measured neutral current, NI_PCF, deviates from the sum
of CI_PCF current channel waveforms, there
may be a fault in the system.
To determine how large the mismatch is between the measured
neutral current and the measured A, B, and C currents, select
ISUM_CFG[1:0] to 01 or 10 based on the direction of the neutral
current with respect to the other current channel waveforms.
Table 10. I
SUM
Configuration Options
CONFIG0.
ISUM_CFG[1:0]
ISUM calculation
00, 11
ISUM = CI_PCF
01
ISUM = NI_PCF
10
ISUM = CI_PCF − NI_PCF
ISUMRMS has the same scaling as xIRMS. Note that if AI_PCF,
BI_PCF, and CI_PCF are all at full scale and in phase with each
other, with the ISUM_CFG[1:0] equal to 00 or 11, ISUMRMS is
3 × 52,702,092 = 158,106,276 (decimal). If AI_PCF, BI_PCF,
CI_PCF, and NI_PCF are all at full scale and in phase with each
other, with the ISUM_CFG[1:0] equal to 01, ISUMRMS is
4 × 52,702,092 = 210,808,368 (decimal).
To obtain an indication if ISUMRMS exceeds a threshold,
configure ISUMLVL. Then the MISMTCH bit in STATUS0
and associated interrupt indicate if there is a change in the
relationship between ISUMRMS and ISUMLVL.
Calculate the desired value of ISUMLVL according to the
following equation:
=
X
SCALE
FULL
xIRMS
ISUMLVL
_
_
where:
xIRMS_Full_Scale
is the nominal xIRMS value with full-scale
inputs, 52,702,092.
X
is the desired current level to indicate a MISMTCH error.
For example, to set ISUMLVL to warn about a vector current
sum greater than 10,000:1 from full scale, X = 10,000 in the
previous equation.
Total Active Power
Total active power is commonly used for billing purposes. It
includes power on the fundamental and on the harmonics.
The total active power on each phase is calculated by first
multiplying the xI_PCF and xV_PCF waveforms. Then the
result is low-pass filtered, unless the DISAPLPF bit in the
CONFIG0 register is equal to 1. Finally, the xPGAIN is applied
to perform a gain correction and the xWATTOS value is applied
to correct the watt offset.
Figure 16 shows the relationship between the I and V input
signals and the instantaneous active power and low-pass filtered
active power, assuming that I and V are at full scale with only
the fundamental is present and a power factor of 1.
If the DISAPLPF bit in the CONFIG0 is equal to 1, xWATT
reflects the instantaneous active power; and if it is equal to 0,
xWATT reflects the low-pass filtered active power, in Figure 16,
assuming xPGAIN = 0 and xWATTOS = 0.
–0.062%
+0.062%
LOW-PASS FILTERED
ACTIVE POWER
20,694,066
0
INSTANTANEOUS
ACTIVE POWER
I, V FUNDAMENTAL
INPUT SIGNAL
Figure 16. Instantaneous Active Power and Low-Pass Filtered Active Power at
a Power Factor of 1
The low-pass filter, LPF2, extracts the total active power,
attenuating harmonics of a 50 Hz or 60 Hz fundamental by
64 dB so that, at full scale, the variation in the low-pass filtered
active power is very small, ±0.062%.
The resulting xWATT signal has an update rate of 8 ksps and a
bandwidth of 3.2 kHz.
The xPGAIN register has the same scaling as the xIGAIN
register. xWATTOS has the same scaling as xWATT. xWATT
can be calibrated using the energy or power registers. When
using the power registers, xWATTOS is calculated using the
following equation:
xWATTOS
=
xWATT
EXPECTED
−
xWATT
MEASURED
The xWATT value with full-scale inputs and no gain is
20,694,066. Note that xVAR and VA have the same scaling;
therefore, the same equation can be used for all three offsets.
