ADE7752B_15 datasheet(19/24 Pages) AD

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ADE7752B

Rev. 0 | Page 19 of 24

ACCUMULATION OF 3-PHASE POWER

Power Measurement Considerations

Calculating and displaying power information always have some

associated ripple that depends on the integration period used in the

MCU to determine average power as well as the load. For example,

at light loads, the output frequency can be 10 Hz. With an integra-

tion period of 2 seconds, only about 20 pulses are counted. The

possibility of missing one pulse always exists because the

ADE7752B output frequency is running asynchronously to the

MCU timer. This results in a 1-in-20 or 5% error in the power

measurement. To remedy this, an appropriate integration time

should be considered to achieve the desired accuracy.

Mode Selection of the Sum of the Three Active Energies

The ADE7752B can be configured to execute the arithmetic

sum of the three active energies, Wh = WhΦA + WhΦB + WhΦC,

or the sum of the absolute value of these energies, Wh = |WhΦA|

+ |WhΦB| + |WhΦC|. The selection between the two modes can

be made by setting the ABS pin. Logic high and logic low

applied on the ABS pin correspond to the arithmetic sum and

the sum of absolute values, respectively.

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 3-phase, 4-wire installa-

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

same. If the meter is misconnected to the power lines, that is, if

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 assures that the active energy

recorded represents the actual active energy delivered. In this

mode, the reverse power pin still detects when the arithmetic

sum of the active powers is negative, but energy continues to

accumulate regardless of the sign.

Negative Total Power Detection

The ADE7752B detects when total power, calculated as the

arithmetic sum of the three phases, is negative. This detection

is independent of the mode of sum of the three powers (arithmetic

or absolute). This mechanism can detect an incorrect connec-

tion of the meter or generation of negative active energy. When

the sum of the powers of the three phases is negative, the REVP

pin output goes active high. When the sum of the powers of the

three phases is positive, the REVP pin output is reset to low.

The REVP pin output changes state at the same time as a pulse

is issued on CF. If the sum of the powers of the three phases is

negative, then the REVP pin output stays high until the sum is

positive or all three phases are below the no-load threshold.

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