ADE7755
Using Equations 1 and 2, the real power P can be expressed in
terms of its fundamental real power (P1) and harmonic real
power (PH).
Table I. Gain Selection for Channel 1
Maximum
Differential Signal
G1
G0
Gain
P = P + PH
1
0
0
1
1
0
1
0
1
1
2
8
16
±470 mV
±235 mV
±60 mV
±30 mV
where:
P = V1 ¥ I1 cos f1
1
(3)
f1 = a1 – b1
Channel V2 (Voltage Channel)
and:
The output of the line voltage transducer is connected to the
ADE7755 at this analog input. Channel V2 is a fully differential
voltage input. The maximum peak differential signal on
Channel 2 is ± 660 mV. Figure 5 illustrates the maximum
signal levels that can be connected to the ADE7755 Channel 2.
PH
=
• Vh ¥ Ihcosfh
Â
hπ1
(4)
fh = ah – bh
As can be seen from Equation 4 above, a harmonic real power
component is generated for every harmonic, provided that har-
monic 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; therefore the harmonic
real power must also correctly account for the power factor
since it is made up of a series of pure sinusoids.
V2
+660mV
V2P
V2N
DIFFERENTIAL INPUT
V2
ꢃ660mV MAX PEAK
V
CM
COMMON-MODE
V
CM
ꢃ100mV MAX
Note that the input bandwidth of the analog inputs is 14 kHz
with a master clock frequency of 3.5795 MHz.
AGND
–660mV
ANALOG INPUTS
Channel V1 (Current Channel)
Figure 5. Maximum Signal Levels, Channel 2
The voltage output from the current transducer is connected to
the ADE7755 here. Channel V1 is a fully differential voltage
input. V1P is the positive input with respect to V1N.
Channel 2 must be driven from a common-mode voltage, i.e.,
the differential voltage signal on the input must be referenced to
a common mode (usually AGND). The analog inputs of the
ADE7755 can be driven with common-mode voltages of up to
100 mV with respect to AGND. However, best results are
achieved using a common mode equal to AGND.
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 I). These gains facilitate easy transducer interfacing.
Typical Connection Diagrams
Figure 6 shows a typical connection diagram for Channel V1. A
CT (current transformer) is the current transducer selected for this
example. Notice the common-mode voltage for Channel 1 is
AGND and is derived by center tapping the burden resistor to
AGND. This provides the complementary analog input signals
for V1P and V1N. The CT turns ratio and burden resistor Rb
are selected to give a peak differential voltage of ±470 mV/Gain
at maximum load.
V1
+470mV
V1P
V1N
DIFFERENTIAL INPUT
V1
ꢃ470mV MAX PEAK
V
CM
COMMON-MODE
V
CM
ꢃ100mV MAX
AGND
–470mV
Rf
V1P
V1N
CT
Cf
Cf
ꢃ470mV
GAIN
Rb
Figure 4. Maximum Signal Levels, Channel 1, Gain = 1
AGND
IP
Rf
The diagram in Figure 4 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, e.g., AGND.
The maximum common-mode signal is ±100 mV as shown in
Figure 4.
PHASE NEUTRAL
Figure 6. Typical Connection for Channel 1
REV. 0
–11–
ADI [ ADI ]
