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ADE7762

Polyphase Energy Metering IC with Phase Drop Indication

Analog Devices 

ADE7762

HPF AND OFFSET EFFECTS

Figure 27 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 27. 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.

{V cos(ωt ) + VOS }× {I cos(ωt ) + IOS }=

V×I

2

+ VOS

× I OS

+ VOS

× I cos(ωt ) + IOS ×V

cos(ωt )

(9)

+ V × I × cos(2ωt )

2

VOS × IOS

V× I

2

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR REAL

POWER CALCULATION

Preliminary Technical Data

The ADE7762 is phase compensated up to 1 kHz as shown. This

ensures correct active harmonic power calculation even at low

power factors.

Figure 28. Phase Error between Channels (0 Hz to 1 kHz)

IOS × V

VOS × I

0

ω

2ω

FREQUENCY – RAD/S

Figure 27. 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 28 and Figure 29 show the

phase error between channels with the compensation network.

Figure 29. Phase Error Between Channels (40 Hz to 70 Hz)

Rev. PrB | Page 20 of 28

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