EVAL-ADE7755ZEB Datasheet, PDF (13/20 Pages) Analog Devices – Energy Metering IC with Pulse Output

NONSINUSOIDAL VOLTAGE AND CURRENT
The active power calculation method also holds true for non-
sinusoidal current and voltage waveforms. All voltage and current
waveforms in practical applications have some harmonic content.
Using the Fourier Transform operation, instantaneous voltage
and current waveforms can be expressed in terms of their
harmonic content.
( ) ^∞
v(t) = V_O + 2 × _∑V_h × sin hωt + a_h
(1)
h≠0
where:
v(t) is the instantaneous voltage.
VO is the average voltage value.
Vh is the rms value of the voltage harmonic, h.
ah is the phase angle of the voltage harmonic.
∞
i(t) = I_O + 2 × _∑ I_h × sin(hωt + β_h)
(2)
h≠0
where:
i(t) is the instantaneous current.
IO is the current dc component.
Ih is the rms value of the current harmonic, h.
βh is the phase angle of the current harmonic.
Using Equation 1 and Equation 2, the active power (P) can be
expressed in terms of its fundamental active power (P1) and
harmonic active power (PH).
P = P1 + PH
(3)
where:
P1 is the active power of the fundamental component:
P1 = V1 × I1 cosΦ1
Φ1 = α1 – β1
and
PH is the active power of all harmonic components:
∞
PH = ∑Vh × Ih cos Φh
h≠1
Φh = αh – βh
ADE7755
A harmonic active power component is generated for every
harmonic, provided that the harmonic is present in both the
voltage and current waveforms. The power factor calculation
previously shown is accurate in the case of a pure sinusoid;
therefore, the harmonic active power must also correctly
account for the power factor because it is made up of a series of
pure sinusoids.
Note that the input bandwidth of the analog inputs is 14 kHz
with a master clock frequency of 3.5795 MHz.
ANALOG INPUTS
Channel 1 (Current Channel)
The voltage output from the current transducer is connected
to the ADE7755 at Channel 1. Channel 1 is a fully differential
voltage input. V1P is the positive input with respect to V1N.
The maximum peak differential signal on Channel 1 should be
less than ±470 mV (330 mV rms for a pure sinusoidal signal)
for specified operation. Note that Channel 1 has a programmable
gain amplifier (PGA) with user-selectable gain of 1, 2, 8, or 16
(see Table 5). These gains facilitate easy transducer interfacing.
V1
+470mV
V_CM
DIFFERENTIAL INPUT
±470mV MAX PEAK
COMMON-MODE
±100mV MAX
V1P
V1 _V1N
V_CM
–470mV
AGND
Figure 24. Maximum Signal Levels, Channel 1, Gain = 1
Figure 24 illustrates the maximum signal levels on V1P and
V1N. The maximum differential voltage is ±470 mV divided by
the gain selection. The differential voltage signal on the inputs
must be referenced to a common mode, for example, AGND.
The maximum common-mode signal is ±100 mV, as shown in
Figure 24.
Table 5. Gain Selection for Channel 1
G1 G0 Gain Maximum Differential Signal (mV)
001
±470
012
±235
108
±60
1 1 16
±30
Rev. A | Page 13 of 20