ADE7880 datasheet(48/104 Pages) AD

48 / 104 page

ADE7880

Data Sheet

Rev. A | Page 48 of 104

Energy Accumulation Modes

The active power is accumulated in each watt-hour

accumulation 32-bit register (AWATTHR, BWATTHR,

CWATTHR, AFWATTHR, BFWATTHR, and CFWATTHR)

according to the configuration of Bit 5 and Bit 4 (CONSEL bits) in

the ACCMODE register. The various configurations are described

in Table 14.

Table 14. Inputs to Watt-Hour Accumulation Registers

CONSEL

AWATTHR

BWATTHR

CWATTHR

VA × IA

VB × IB

VC × IC

VA × IA

VB × IB

VB = VA – VC1

VC × IC

VA × IA

VB × IB

VC × IC

VB = −VA − VC

VA × IA

VB × IB

VC × IC

VB = −VA

1 In a 3-phase three wire case (CONSEL[1:0] = 01), the ADE7880 computes the

rms value of the line voltage between Phase A and Phase C and stores the

result into BVRMS register (see the Voltage RMS in 3-Phase Three Wire Delta

Configurations section). Consequently, the ADE7880 computes powers

associated with Phase B that do not have physical meaning. 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 bits TERMSEL1[1] or TERMSEL2[1] or

TERMSEL3[1] to 0 in the COMPMODE register (see the Energy-to-Frequency

Conversion section).

Depending on the polyphase meter service, choose the appro-

priate formula to calculate the active energy. The American

ANSI C12.10 standard defines the different configurations of

the meter. Table 15 describes which mode to choose in these

various configurations.

Table 15. Meter Form Configuration

ANSI Meter Form

Configuration

CONSEL

5S/13S

3-wire delta

6S/14S

4-wire wye

8S/15S

4-wire delta

9S/16S

4-wire wye

Bits[1:0] (WATTACC[1:0]) in the ACCMODE register determine

how the active power is accumulated in the watt-hour registers

and how the CF frequency output can be generated as a

function of the total and fundamental active powers. See the

Energy-to-Frequency Conversion section for details.

Line Cycle Active Energy Accumulation Mode

In line cycle energy accumulation mode, the energy accumula-

tion is synchronized to the voltage channel zero crossings such

that active energy is accumulated over an integral number of

half line cycles. The advantage of summing the active energy

over an integer number of line cycles is that the sinusoidal compo-

nent in the active 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. By using the line

cycle energy accumulation mode, the energy calibration can be

greatly simplified, and the time required to calibrate the meter

can be significantly reduced. In line cycle energy accumulation

mode, the ADE7880 transfers the active energy accumulated in the

32-bit internal accumulation registers into the xWATHHR or

xFWATTHR registers after an integral number of line cycles, as

shown in Figure 76. The number of half line cycles is specified

in the LINECYC register.

The line cycle energy accumulation mode is activated by setting

Bit 0 (LWATT) in the LCYCMODE register. The energy accu-

mulation over an integer number of half line cycles is written

to the watt-hour accumulation registers after LINECYC number

of half line cycles is detected. When using the line cycle

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

watt-hour registers is not available in this mode.

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

included when counting the number of half line cycles by setting

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

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

for counting the zero crossing. Select only one phase at a time

for inclusion in the zero crossings count during calibration.

ZERO-

CROSSING

DETECTION

(PHASE A)

ZERO-

CROSSING

DETECTION

(PHASE B)

CALIBRATION

CONTROL

ZERO-

CROSSING

DETECTION

(PHASE C)

LINECYC[15:0]

AWATTHR[31:0]

ZXSEL[0] IN

LCYCMODE[7:0]

ZXSEL[1] IN

LCYCMODE[7:0]

ZXSEL[2] IN

LCYCMODE[7:0]

OUTPUT

FROM

LPF2

AWGAIN AWATTOS

INTERNAL

ACCUMULATOR

THRESHOLD

32-BIT

WTHR

27 26

Figure 76. Line Cycle Active Energy Accumulation Mode

The number of zero crossings is specified by the LINECYC 16-bit

unsigned register. The ADE7880 can accumulate active power

for up to 65,535 combined zero crossings. Note that the internal

zero-crossing counter is always active. By setting Bit 0 (LWATT)

in the LCYCMODE register, the first energy accumulation

result is, therefore, incorrect. Writing to the LINECYC register

when the LWATT bit is set resets the zero-crossing counter, thus

ensuring that the first energy accumulation result is accurate.

At the end of an energy calibration cycle, Bit 5 (LENERGY) in

the STATUS0 register is set. If the corresponding mask bit in

the MASK0 interrupt mask register is enabled, the IRQ0 pin

also goes active low. The status bit is cleared and the IRQ0 pin is

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