BL0921

BL0921

BL0921

BL0921

http://www.belling.com.cn

- 6 -

3/15/2007

Total 13 Pages

Single Phase Energy Meter IC

Single Phase Energy Meter IC

Single Phase Energy Meter IC

Single Phase Energy Meter IC

with Integrated Oscillator

with Integrated Oscillator

with Integrated Oscillator

with Integrated Oscillator

)

2

cos(

1

(

2

)

(

wt

VI

t

p

+

=

≠

[

]

)

sin(

)

2

sin(

2

)

cos(

))

2

cos(

1

(

2

)

sin(

)

sin(

)

cos(

)

cos(

))

2

cos(

1

(

2

)

sin(

)

sin(

)

cos(

)

cos(

)

cos(

)

cos(

)

cos(

)

(

Φ

+

Φ

+

=

Φ

+

Φ

+

=

Φ

+

Φ

×

=

Φ

+

×

=

wt

VI

wt

VI

wt

wt

VI

wt

VI

wt

wt

I

wt

V

wt

I

wt

V

t

p

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:

cos( )

2

VI

P

ϕ

=

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 BL0921, 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

extract the real power component (i.e., the dc component), the instantaneous power signal is

low-pass filtered. Figure 2 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