ADE9078ACPZ datasheet(38/108 Pages) AD

38 / 108 page

Data Sheet

ADE9078

Rev. 0 | Page 37 of 107

at full scale and in phase with each other, with the ISUM_CFG = 01

then ISUMRMS is 4 × 52,866,837d = 211,467,348d.

To receive an indication if ISUMRMS exceeds a threshold,

configure ISUMLVL. 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:













SCALE

FULL

xIRMS

ISUMLVL

where:

xIRMS_FULL_SCALE is the nominal xIRMS value with full-

scale inputs, 52,866,837.

X is the desired current level to indicate a MISMTCH error. For

example, set the ISUMLVL to warn about a rms of sum of

instantaneous currents greater than 10,000:1 from full scale, X =

10,000.

Total Active Power

Total active power is commonly used for billing purposes. It

includes power on the fundamental and on the harmonics.

Figure 55 shows how the low-pass filtered total active power on

Phase A is calculated. First, the AI_PCF and AV_PCF waveforms

are multiplied together. Then, the result is low-pass filtered,

unless DISAPLPF = 1. Finally, the APGAIN is applied to perform

a gain correction and the AWATTOS value is applied to correct

the active power offset.

APGAIN

AWATTOS

AWATT

LPF2

DISAPLPF

AI_PCF

AV_PCF

ENERGY/

POWER/

CF ACCUMULATION

Figure 55. Total Active Power (AWATT) Calculation

Figure 56 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 just the

fundamental present and a power factor of 1.

If DISAPLPF = 1, AWATT reflects the instantaneous active

power and if it is 0, AWATT reflects the low-pass filtered active

power in Figure 56, assuming that APGAIN = 0 and

AWATTOS = 0.

–0.062%

+0.062%

LOW-PASS FILTERED

ACTIVE POWER

20,823,646

INSTANTANEOUS

ACTIVE POWER

I, V FUNDAMENTAL

INPUT SIGNAL

Figure 56. 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 AWATT signal has an update rate of 4 kSPS and a

bandwidth of 1.6 kHz, as given in Table 1.

Phase B and Phase C have similar datapaths to those described

for AWATT to calculate BWATT and CWATT, with individual

gain and phase coefficients, BPGAIN and BWATTOS, and

CPGAIN, and CWATTOS.

The xPGAIN register has the same scaling as the xIGAIN

xIGAIN section).

Note that for a given phase,

|Current Channel Gain × Voltage Channel Gain ×

Power Gain| ≤ 3.75

xWATTOS has the same scaling as xWATT. To understand how

xWATTOS affects the xWATT value, use the following

equation:

















SCALE

FULL

xWATT

xWATTOS

where:

xWATT_FULL_SCALE is the nominal xWATT value with full-

scale inputs, 20,823,646. Note that xVAR and VA have the same

scaling, so the same equation can be used for all three offsets.

X is the smallest power level to calibrate. For example, to

calibrate the energy at 10,000 from full scale, X = 10,000.

000

20,823,646













xWATTOS

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