ADE7754_15 datasheet(22/44 Pages) AD

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REV. 0

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ADE7754

by setting to Logic 1 Bit 3 of the gain register (Address 18h). See

Table X. Any load generating an active power amplitude lower

than the minimum amplitude specified will not be taken into

account when accumulating the active power from this phase.

The minimum instantaneous active power allowed in this mode

is 0.005% of the full-scale amplitude. Because the maximum

active power value is 13,743,895d with full-scale analog input,

the no-load threshold is 687d. For example, an energy meter

with maximum inputs of 220 V and 40 A and Ib = 10 A, the

maximum instantaneous active power is 3,435,974d, assuming

that both inputs represent half of the analog input full scale. As

the no-load threshold represents 687d, the start-up current

represents 8 mA or 0.08% of Ib.

Mode Selection of the Sum of the Three Active Energies

The ADE7754 can be configured to execute the arithmetic sum

of the three active energies, Wh = Wh A + Wh B + Wh C, or the

sum of the absolute value of these energies, Wh = |Wh A| +

|Wh B| + |Wh C|. The selection between the two modes can

be made by setting Bit 2 of the gain register (Address 18h). See

Table X. Logic high and logic low of this bit correspond to the

sum of absolute values and the arithmetic sum, respectively.

This selection affects the active energy accumulation in the

AENERGY, RAENERGY, and LAENERGY registers as well

as the CF frequency output.

When the sum of the absolute values is selected, the active

energy from each phase is always counted positive in the total

active energy. It is particularly useful in a 3-phase, 4-wire instal-

lation where the sign of the active power should always be the

same. If the meter is misconnected to the power lines (e.g., CT

is connected in the wrong direction), the total active energy

recorded without this solution can be reduced by two thirds. The

sum of the absolute values ensures that the active energy recorded

represents the actual active energy delivered. In this mode, the

reverse power information available in the CFNUM register is

still detecting when negative active power is present on any of

the three phase inputs.

LINE ENERGY ACCUMULATION

The ADE7754 is designed with a special energy accumulation

mode that simplifies the calibration process. By using the on-

chip zero-crossing detection, the ADE7754 accumulates the

active power signal in the LAENERGY register for an integer

number of half cycles, as shown in Figure 31. The line active

energy accumulation mode is always active.

Using this mode with only one phase selected is recommended.

If several phases are selected, the amount accumulated may be

smaller than it should be.

Each one of three phases zero-crossing detection can contribute

to the accumulation of the half line cycles. Phase A, B, and C

zero crossings, respectively, are taken into account when count-

ing the number of half line cycles by setting Bits 4 to 6 of the

MMODE register to Logic 1. Selecting phases for the zero-

crossing counting also has the effect of enabling the zero-cross-

ing detection, zero-crossing timeout and period measurement

for the corresponding phase as described in the zero-crossing

detection paragraph.

The number of half line cycles is specified in the LINCYC

can accumulate active power for up to 65535 combined half

cycles. Because the active power is integrated on an integer

number of line cycles, the sinusoidal component is reduced to

zero. This eliminates any ripple in the energy calculation. Energy

is calculated more accurately because of this precise timing

control. At the end of an energy calibration cycle, the LINCYC

flag in the interrupt status register is set. If the LINCYC enable

bit in the interrupt enable register is set to Logic 1, the

IRQ

output also goes active low.

AENERGY[23:0]

WDIV

POWER

PHASE B

POWER

PHASE A

POWER

PHASE C

LPF1

FROM VA

ADC

ZERO-CROSS

DETECT

MMODE

LPF1

FROM VB

ADC

ZERO-CROSS

DETECT

MMODE

LPF1

FROM VC

ADC

ZERO-CROSS

DETECT

MMODE

CALIBRATION

CONTROL

LINCYC[15:0]

ACCUMULATE ACTIVE POWER

DURING LINCYC ZERO CROSSINGS

Figure 31. Active Energy Calibration

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