ADE7763ARS datasheet(29/56 Pages) AD

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ADE7763

Rev. A | Page 29 of 56

The active power signal (output of LPF2) can be rewritten as

)

cos(

)

(

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

(18)

where fL is the line frequency, for example, 60 Hz.

From Equation 13,

)

sin(

)

(

VIt

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

−

(19)

Note that in Equation 19 there is a small ripple in the energy

calculation due to a sin(2ωt) component. This is shown graphi-

cally in Figure 60. The active energy calculation is represented

by the dashed, straight line and is equal to V × I × t. The sinu-

soidal ripple in the active energy calculation is also shown.

Because the average value of a sinusoid is 0, the ripple does not

contribute to the energy calculation over time. However, the

ripple might be observed in the frequency output, especially at

higher output frequencies. The ripple becomes larger as a

percentage of the frequency at larger loads and higher output

frequencies. This occurs because the integration or averaging

time in the energy-to-frequency conversion process is shorter at

higher output frequencies. Consequently, some of the sinusoidal

ripple in the energy signal is observable in the frequency output.

Choosing a lower output frequency at CF for calibration can

significantly reduce the ripple. Also, averaging the output

frequency by using a longer gate time for the counter achieves

the same results.

–

sin(4

×π×f

L×t)

×π×f

L(1+2×fL/8. 9Hz )

E(t)

Vlt

Figure 60. Output Frequency Ripple

WDIV[7:0]

APOS[15:0]

WGAIN[11:0]

LPF1

LAENERGY[23:0]

ACCUMULATE ACTIVE

ENERGY IN INTERNAL

THE LAENERGY REGISTER

AT THE END OF LINECYC

LINE CYCLES

OUTPUT

FROM

LPF2

FROM

CHANNEL 2

ADC

LINECYC[15:0]

ZERO CROSSING

DETECTION

CALIBRATION

CONTROL

Figure 61. Energy Calculation Line Cycle Energy Accumulation Mode

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