ADE7760

Rev. 0 | Page 15 of 24

The HPF in Channel 1 has an associated phase response that is

compensated for on-chip. Figure 20 and Figure 21 show the

phase error between channels with the compensation network

activated. The ADE7760 is phase compensated up to 1 kHz as

shown, which ensures correct active harmonic power

calculation even at low power factors.

DC COMPONENT (INCLUDING ERROR TERM)

IS EXTRACTED BY THE LPF FOR ACTIVE

POWER CALCULATION

2v

FREQUENCY (RAD/S)

0v

2

Figure 19. Effect of Channel Offsets on the Active Power Calculation

FREQUENCY (Hz)

0

100

–0.05

–0.10

0

0.05

0.10

0.15

0.20

0.25

0.30

200

300

400

500

600

700

800

900

1000

Figure 20. Phase Error between Channels (0 Hz to 1 kHz)

FREQUENCY (Hz)

40

–0.05

–0.10

0.05

0

0.10

0.15

0.20

0.25

0.30

45

50

55

60

65

70

Figure 21. Phase Error between Channels (40 Hz to 70 Hz)

DIGITAL-TO-FREQUENCY CONVERSION

As previously described, the digital output of the low-pass filter

after multiplication contains the active power information.

However, because this LPF is not an ideal “brick wall” filter

implementation, the output signal also contains attenuated

components at the line frequency and its harmonics, that is,

cos(hωt), where h = 1, 2, 3, ..., and so on. The magnitude

response of the filter is given by

2

)

Hz

5

.

4

/

(

1

1

)

(

f

f

H

=

=

(6)

For a line frequency of 50 Hz, this gives an attenuation of the 2ω

(100 Hz) component of approximately –26.9 dB. The dominat-

ing harmonic is at twice the line frequency, that is, cos(2ωt), due

to the instantaneous power signal.

Figure 22 shows the instantaneous active power signal output of

the LPF, which still contains a significant amount of instantane-

ous power information, cos(2ωt). This signal is then passed to

the digital-to-frequency converter, where it is integrated

(accumulated) over time to produce an output frequency. This

accumulation of the signal suppresses or averages out any non-

dc components in the instantaneous active power signal. The

average value of a sinusoidal signal is zero. Therefore, the

frequency generated by the ADE7760 is proportional to the

average active power.

Figure 22 also shows the digital-to-frequency conversion for

steady load conditions: constant voltage and current. As can be

seen in Figure 22, the frequency output CF varies over time,

even under steady load conditions. This frequency variation is

primarily due to the cos(2ωt) component in the instantaneous

active power signal.

F1

F2

CF

DIGITAL-TO-

FREQUENCY

DIGITAL-TO-

FREQUENCY

MULTIPLIER

LPF

V

I

0

ϖ

2

ϖ

FREQUENCY (Rad/s)

LPF TO EXTRACT

ACTIVE POWER

(DC TERM)

TIME

TIME

F1

FOUT

INSTANTANEOUS ACTIVE POWER SIGNAL (FREQUENCY DOMAIN)

Figure 22. Active Power to Frequency Conversion