EVAL-ADE7763EB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-ADE7763EB' PDF : 56 Pages View PDF
0.4
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0.1
0.0
–0.1
–0.2
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54
56
58
60
62
64
66
FREQUENCY (Hz)
Figure 52. Combined Gain Response of HPF and Phase Compensation
ACTIVE POWER CALCULATION
Power is defined as the rate of energy flow from the source to
the load. It is defined as the product of the voltage and current
waveforms. The resulting waveform is called the instantaneous
power signal and is equal to the rate of energy flow at any given
time. The unit of power is the watt or joules/s. Equation 9 gives
an expression for the instantaneous power signal in an ac system.
v(t) = 2 ×V sin(ωt)
(7)
i(t) = 2×I sin(ω t)
(8)
where:
V is the rms voltage.
I is the rms current.
p(t) = v(t) × i(t)
p(t) = VI −VI cos(2ωt)
(9)
The average power over an integral number of line cycles (n) is
given by the expression in Equation 10.
∫ P = 1
nT
p(t)dt = VI
nT 0
(10)
where:
T is the line cycle period.
P is the active or real power.
Note that the active power is equal to the dc component of the
instantaneous power signal p(t) in Equation 8, i.e., VI. This is
the relationship used to calculate active power in the ADE7763.
ADE7763
The instantaneous power signal p(t) is generated by multiplying
the current and voltage signals. The dc component of the instan-
taneous power signal is then extracted by LPF2 (low-pass filter)
to obtain the active power information. This process is illustrated
in Figure 53.
INSTANTANEOUS
POWER SIGNAL
0x19 999A
p(t) = v × i-v × i × cos(2ωt)
ACTIVE REAL POWER
SIGNAL = v × i
VI
0xC CCCD
0x0 0000
CURRENT
i(t) = 2 × i × sin(ωt)
VOLTAGE
v(t) = 2 × v × sin(ωt)
Figure 53. Active Power Calculation
Because LPF2 does not have an ideal “brick wall” frequency
response (see Figure 54), the active power signal has some
ripple due to the instantaneous power signal. This ripple is
sinusoidal and has a frequency equal to twice the line frequency.
Because the ripple is sinusoidal in nature, it is removed when the
active power signal is integrated to calculate energy—see the
Energy Calculation section.
0
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–8
–12
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–24
1
3
10
30
100
FREQUENCY (Hz)
Figure 54. Frequency Response of LPF2
Rev. A | Page 25 of 56
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