BL6506
p
(
t
)
=
V
cos(
wt
)
×
I
cos(
wt
+ Φ
)
Single Phase Energy Meter IC
with Integrated Oscillator
current signal and the voltage signal is expressed asФ. Then the power is given as follows:
Φ
=0:
p
(
t
)
=
Φ ≠
0:
VI
(1
+
cos(2
wt
)
2
p
(
t
)
=
V
cos(
wt
)
×
I
cos(
wt
+ Φ
)
=
V
cos(
wt
)
×
[
I
cos(
wt
) cos(
Φ
)
+
sin(
wt
) sin(
Φ
)
]
VI
(1
+
cos(2
wt
)) cos(
Φ
)
+
VI
cos(
wt
) sin(
wt
) sin(
Φ
)
2
VI
VI
=
(1
+
cos(2
wt
)) cos(
Φ
)
+
sin(2
wt
) sin(
Φ
)
2
2
=
p(t) is called as the instantaneous power signal. The ideal p(t) consists of the dc component and ac
component whose frequency is 2ω. The dc component is called as the average active power, that
is:
P
=
VI
cos(
ϕ
)
2
The average active power is related to the cosine value of the phase difference between the voltage
signal and the current signal. This cosine value is called as Power Factor (PF) of the two channel
signals.
Figure1.
The Effect of phase
When the signal phase difference between the voltage and current channels is more than 90°, the
average active power is negative. It indicates the user is using the electrical energy reversely.
Operation Process
In BL6506, the two ADCs digitize the voltage signals from the current and voltage transducers.
These ADCs are 16-bit second order sigma-delta with an over sampling rate of 900 kHz. This
analog input structure greatly simplifies transducer interfacing by providing a wide dynamic range
for direct connection to the transducer and also simplifying the anti-alias filter design. A
programmable gain stage in the current channel further facilitates easy transducer interfacing. A
high pass filter in the current channel removes any dc component from the current signal. This
eliminates any inaccuracies in the real power calculation due to offsets in the voltage or current
signals.
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. In order to
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-6-
Total
14 Pages
3/15/2007
BELLING [ SHANGHAI BELLING CO., LTD. ]
