ADE7752B_15 datasheet(17/24 Pages) AD

17 / 24 page

ADE7752B

Rev. 0 | Page 17 of 24

HPF AND OFFSET EFFECTS

Figure 20 shows the effect of offsets on the active power

calculation. An offset on the current channel and the voltage

channel contributes a dc component after multiplication, as

shown in Figure 20. Because this dc component is extracted by

the LPF and is used to generate the active power information

for each phase, the offsets can contribute a constant error to the

total active power calculation. The HPF in the current channels

avoids this problem easily. By removing the offset from at least

one channel, no error component can be generated at dc by the

multiplication. Error terms at cos(ωt) are removed by the LPF

and the digital-to-frequency conversion (see the Digital-to-

Frequency Conversion section).

( )

{

}

( )

{

}

()

( )

()

cos

(10)

VOS ×IOS

VOS × I

IOS × V

2ω

FREQUENCY (RAD/sec)

V× I

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR REAL

POWER CALCULATION

Figure 20. Effect of Channel Offset on the Active Power Calculation

The HPF in the current channels has an associated phase response

that is compensated for on-chip. Figure 21 and Figure 22 show the

phase error between channels with the compensation network.

The ADE7752B is phase compensated up to 1 kHz as shown. This

ensures correct active harmonic power calculation even at low

power factors.

FREQUENCY (Hz)

0.07

0.06

–0.01

1000

200

400

600

800

0.03

0.02

0.01

0.05

0.04

100

300

500

700

900

Figure 21. Phase Error Between Channels (0 Hz to 1 kHz)

FREQUENCY (Hz)

0.010

0.008

–0.004

0.002

–0.002

0.006

0.004

Figure 22. Phase Error Between Channels (40 Hz to 70 Hz)

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