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ADE7752A Datasheet(PDF) 12 Page - Analog Devices

Part No. ADE7752A
Description  Polyphase Energy Metering IC with Pulse Output
Download  24 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADE7752A Datasheet(HTML) 12 Page - Analog Devices

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ADE7752/ADE7752A
Rev. C | Page 12 of 24
THEORY OF OPERATION
The six voltage signals from the current and voltage transducers
are digitized with ADCs. These ADCs are 16-bit second-order
∑-Δ with an oversampling rate of 833 kHz. This analog input
structure greatly simplifies transducer interface by providing a
wide dynamic range for direct connection to the transducer and
also by simplifying the antialiasing filter design. A high-pass
filter in the current channel removes the dc component from
the current signal. This eliminates any inaccuracies in the real
power calculation due to offsets in the voltage or current
signals. See the
The low frequency output of the ADE7752 is generated by
accumulating the total real power information. This low
frequency inherently means a long accumulation time between
output pulses. The output frequency is therefore proportional to
the average real power. This average real power information
can, in turn, be accumulated (by a counter, for example) to
generate real energy information. Because of its high output
frequency and therefore shorter integration time, the CF output
is proportional to the instantaneous real power. This pulse is
useful for system calibration purposes that would take place
under steady load conditions.
HPF and Offset Effects section.
The real power calculation is derived from the instantaneous
power signal. The instantaneous power signal is generated by a
direct multiplication of the current and voltage signals of each
phase. In order to extract the real power component (the dc
component), the instantaneous power signal is low-pass filtered
on each phase.
POWER FACTOR CONSIDERATIONS
Low-pass filtering, the method used to extract the real power
information from the individual instantaneous power signal, is
still valid when the voltage and current signals of each phase are
not in phase.
Figure 15 illustrates the instantaneous real
power signal and shows how the real power information can be
extracted by low-pass filtering the instantaneous power signal.
This method is used to extract the real power information on
each phase of the polyphase system. The total real power
information is then obtained by adding the individual phase
real power. This scheme correctly calculates real power for
nonsinusoidal current and voltage waveforms at all power
factors. All signal processing is carried out in the digital domain
for superior stability over temperature and time.
Figure 16 displays the unity power factor
condition and a DPF (displacement power factor) = 0.5, or
current signal lagging the voltage by 60°, for one phase of the
polyphase. Assuming that the voltage and current waveforms
are sinusoidal, the real power component of the instantaneous
power signal, or the dc term, is given by
()
°
×
⎛ ×
60
cos
2
1
V
TIME
IAP
IAN
VAP
HPF
LPF
IBP
IBN
VBP
ICP
ICN
VCP
VN
DIGITAL-TO-
FREQUENCY
DIGITAL-TO-
FREQUENCY
F1
F2
CF
INSTANTANEOUS
REAL POWER SIGNAL
INSTANTANEOUS
POWER SIGNAL - p(t)
INSTANTANEOUS
TOTAL
POWER SIGNAL
VA
× IA + VB × IB +
VC
×IC
2
ABS
|X|
Σ
Σ
Σ
LPF
LPF
|X|
|X|
p(t) = i(t)
× v(t)
WHERE:
V
× I
2
{1+ cos (2
ωt)}
v(t) = V
× cos (ωt)
i(t) = I
× cos (ωt)
p(t) =
V
× I
2
V
× I
V
× I
2
MULTIPLIER
MULTIPLIER
MULTIPLIER
HPF
HPF
ADC
ADC
ADC
ADC
ADC
ADC
Figure 15. Signal Processing Block Diagram


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