ADE7761ARS-REF Analog Devices Inc, ADE7761ARS-REF Datasheet - Page 17

• Manufacturer Part Number: ADE7761ARS-REF
• Description: IC ENERGY METERING 20-SSOP
• Manufacturer: Analog Devices Inc

Specifications of ADE7761ARS-REF

• Rohs Status: RoHS non-compliant

Using Equations 1 and 2, the active power P can be expressed in
terms of its fundamental active power (P
power (P
where:
and
As can be seen from Equation 4, a harmonic active power
component is generated for every harmonic, provided that
harmonic is present in both the voltage and current waveforms.
The power factor calculation has previously been shown to be
accurate in the case of a pure sinusoid; the harmonic active
power must, therefore, also correctly account for power factor,
because it is made up of a series of pure sinusoids.
Note that the input bandwidth of the analog inputs is 7 kHz
with the internal oscillator frequency of 450 kHz.
HPF and Offset Effects
Equation 5 shows the effect of offsets on the active power
calculation. Figure 22 shows the effect of offsets on the active
power calculation in the frequency domain.
As can be seen from Equation 5 and Figure 22, an offset on
Channel 1 and Channel 2 contributes a dc component after
multiplication. Because this dc component is extracted by the
LPF and used to generate the active power information, the
offsets contribute a constant error to the active power calcula-
tion. This problem is easily avoided in the ADE7761 with the
HPF in Channel 1. 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 Channel 1 has an associated phase response that is
compensated for on-chip. Figure 23 and Figure 24 show the
phase error between channels with the compensation network
activated. The ADE7761 is phase compensated up to 1 kHz as
shown, which ensures correct active harmonic power
calculation even at low power factors.
V
(
V
V
0
) (
P
P
Φ
P
Φ
0
t
×
1
H
+
1
=
h
×
I
=
V
1
=
=
H
=
t I
P
V
) (
):
1
+
1
h
α
α
∑
×
1
∞
=
+
V
1
h
×
2
=
V
cos(
1
P
−
−
I
×
H
h
2
1
β
β
×
cos(
1
I
h
ω
1
I
h
t
+
))
×
Φ
V
×
cos(
1
0
(
)
I
×
0
Φ
I
+
1
h
I
×
)
1
×
cos(
cos(
ω
t
ω
)
t
+
1
))
) and harmonic active
V
=
1
×
I
0
×
cos(
ω
t
)
(5)
(4)
Rev. A | Page 17 of 28
(3)
Figure 22. Effect of Channel Offsets on the Active Power Calculation
–0.05
–0.10
–0.05
–0.10
0.30
0.25
0.20
0.15
0.10
0.05
0.30
0.25
0.20
0.15
0.10
0.05
V
1
0
0
2
× I
40
Figure 24. Phase Error between Channels (40 Hz to 70 Hz)
0
Figure 23. Phase Error between Channels (0 Hz to 1 kHz)
1
0v
100
45
200
DC COMPONENT (INCLUDING ERROR TERM)
IS EXTRACTED BY THE LPF FOR ACTIVE
POWER CALCULATION
300
V
V
50
FREQUENCY (RAD/S)
1
0
FREQUENCY (Hz)
FREQUENCY (Hz)
400
× I
× I
0
1
500
55
2v
600
60
700
800
65
900 1000
ADE7761
70