ADE7752B datasheet(19/27 Pages) AD

19 / 27 page

ADE7752B

Preliminary Technical Data

Rev. PrA | Page 19 of 27

HPF AND OFFSET EFFECTS

Figure 24 shows the effect of offsets on the active power

calculation. An offset on the current channel and voltage

channel contributes a dc component after multiplication as

shown in Figure 24. Since 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

(9)

VOS ×IOS

IOS ×V

VOS ×I

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR REAL

POWER CALCULATION

FREQUENCY – RAD/S

V× I

Figure 24. 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 25 and Figure 26 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.

Figure 25. Phase Error between Channels (0 Hz to 1 kHz)

Figure 26. Phase Error Between Channels (40 Hz to 70 Hz)

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