ade7762 Analog Devices, Inc., ade7762 Datasheet - Page 20

• Manufacturer Part Number: ade7762
• Description: Polyphase Energy Metering Ic With Phase Drop Indication
• Manufacturer: Analog Devices, Inc.

ADE7762
HPF AND OFFSET EFFECTS
Figure 23 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 23. 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.
The HPF in the current channels has an associated phase response
that is compensated for on-chip. Figure 24 and Figure 25 show the
phase error between channels with the compensation network.
Figure 23. Effect of Channel Offset on the Active Power Calculation
(
V
+
V
V
OS
V
2
×
cos
× I
2
I
×
V × I
OS
2
( )
+
I
ω
V
×
0
t
OS
cos
+
×
V
(
2
I
OS
ω
OS
DC COMPONENT (INCLUDING ERROR TERM)
IS EXTRACTED BY THE LPF FOR REAL
POWER CALCULA TION
)
t
×
)
+
ω
(
V
I
I
V
OS
OS
FREQUENCY – RAD/S
cos
OS
× V
×
× I
( )
ω
I
t
cos
+
2 ω
( )
ω
I
OS
t
)
+
=
I
OS
×
V
cos
( )
ω
t
Rev. 0 | Page 20 of 28
(10)
The ADE7762 is phase compensated up to 1 kHz as shown. This
ensures correct active harmonic power calculation even at low
power factors.
–0.002
–0.004
–0.01
0.010
0.008
0.006
0.004
0.002
0.07
0.06
0.05
0.04
0.03
0.02
0.01
Figure 25. Phase Error Between Channels (40 Hz to 70 Hz)
Figure 24. Phase Error Between Channels (0 Hz to 1 kHz)
0
0
0
40
100
45
200
300
50
FREQUENCY (Hz)
FREQUENCY (Hz)
400
500
55
600
60
700
800
65
900
1000
70