ADE7932 datasheet(61/120 Pages) AD

61 / 120 page

Data Sheet

ADE7978/ADE7933/ADE7932

Rev. 0 | Page 61 of 120

ENERGY ACCUMULATION MODES

The reactive power is accumulated in each 32-bit var-hour accu-

mulation register (AVARHR, BVARHR, CVARHR, AFVARHR,

BFVARHR, and CFVARHR) according to the configuration of

Bits[5:4] (CONSEL[1:0] bits) in the ACCMODE register (see

Table 25). Note that IA’, IB’, and IC’ are the phase-shifted current

waveforms.

Table 25. Inputs to Var-Hour Accumulation Registers

CONSEL[1:0]

AVARHR,

AFVARHR

BVARHR,

BFVARHR

CVARHR,

CFVARHR

VA × IA’

VB × IB’

VC × IC’

VA × IA’

VB × IB’

VC × IC’

VB = VA − VC1

Reserved

VA × IA’

VB × IB’

VC × IC’

VB = −VA

See the BWATTHR and BFWATTHR Accumulation Register in 3-Phase, 3-Wire

Configurations section.

Bits[3:2] (VARACC[1:0]) in the ACCMODE register determine

how the reactive power is accumulated in the var-hour registers

and how the CF frequency output can be generated as a function

of total and fundamental active and reactive powers. For more

information, see the Energy-to-Frequency Conversion section.

BWATTHR and BFWATTHR Accumulation Register in

3-Phase, 3-Wire Configurations

In a 3-phase, 3-wire configuration (CONSEL[1:0] = 01), the

ADE7978 computes the rms value of the line voltage between

Phase A and Phase C and stores the result in the BVRMS register

(see the Voltage RMS in Delta Configurations section). The

Phase B current value provided after the HPF is 0; therefore, the

powers associated with Phase B are 0.

To avoid any errors in the frequency output pins (CF1, CF2, or

CF3) related to the powers associated with Phase B, disable the

contribution of Phase B to the energy-to-frequency converters

by setting the TERMSEL1[1], TERMSEL2[1], or TERMSEL3[1]

bit to 0 in the COMPMODE register (Address 0xE60E). For more

information, see the Energy-to-Frequency Conversion section.

LINE CYCLE REACTIVE ENERGY ACCUMULATION

MODE

In line cycle energy accumulation mode, the energy accumulation

is synchronized to the voltage channel zero crossings such that

reactive energy is accumulated over an integral number of half

line cycles. The advantage of summing the reactive energy over

an integer number of line cycles is that the sinusoidal component

in the reactive energy is reduced to 0. This eliminates any ripple

in the energy calculation and allows the energy to be accumulated

accurately over a shorter time. The line cycle energy accumulation

mode greatly simplifies the energy calibration and significantly

reduces the time required to calibrate the meter.

In line cycle energy accumulation mode, the ADE7978 transfers

the reactive energy accumulated in the 32-bit internal accumula-

tion registers to the xVARHR or xFVARHR registers after an

integral number of line cycles (see Figure 80). The number of half

line cycles is specified in the LINECYC register (Address 0xE60C).

ZERO-

CROSSING

DETECTION

(PHASE A)

ZERO-

CROSSING

DETECTION

(PHASE B)

CALIBRATION

CONTROL

ZERO-

CROSSING

DETECTION

(PHASE C)

LINECYC[15:0]

AVARHR[31:0]

ZXSEL[0] IN

LCYCMODE[7:0]

ZXSEL[1] IN

LCYCMODE[7:0]

ZXSEL[2] IN

LCYCMODE[7:0]

OUTPUT FROM

TOTAL REACTIVE

POWER ALGORITHM

APGAIN

AVAROS

INTERNAL

ACCUMULATOR

THRESHOLD

32-BIT

VARTHR

27 26

Figure 80. Line Cycle Total Reactive Energy Accumulation Mode

The line cycle reactive energy accumulation mode is activated by

setting Bit 1 (LVAR) in the LCYCMODE register (Address 0xE702).

The total reactive energy accumulated over an integer number

of half line cycles (or zero crossings) is written to the var-hour

accumulation registers after the number of half line cycles spec-

ified by the LINECYC register is detected. When using the line

cycle accumulation mode, set Bit 6 (RSTREAD) of the LCYCMODE

outside the LINECYC period resets the energy accumulation.

Phase A, Phase B, and Phase C zero crossings are included

when counting the number of half line cycles by setting

Bits[5:3] (ZXSEL[x]) in the LCYCMODE register. Any combi-

nation of zero crossings from all three phases can be used to

count the zero crossings. Select only one phase at a time for

inclusion in the count of zero crossings during calibration.

For more information about setting the LINECYC register and

Bit 5 (LENERGY) in the MASK0 register associated with the

line cycle accumulation mode, see the Line Cycle Active Energy

Accumulation Mode section.

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