BL0921 参数 Datasheet PDF下载

BL0921

current

sampling

analog to

digital

high pass

filter

Single Phase Energy Meter IC

with Integrated Oscillator

scheme correctly calculates real power for non-sinusoidal current and voltage waveforms at all

power factors. All signal processing is carried out in the digital domain for superior stability over

temperature and time.

I

CF

low pass

filter

integral

digital to

frequency

V

voltage

sampling

analog to

digital

high pass

filter

digital

multipli-

cation

F1

F2

instantaneous

power signal p(t)

instantaneous real

power signal

V*I

p(t)=i(t)*v(t)

v(t)=V*cos(wt)

i(t)=I*cos(wt)

p(t)=

t

V*I

2

[1+cos(2wt)]

t

V*I

2

V*I

2

Figure 2.

Signal Processing Block Diagram

Accumulating this real power information generates the low frequency output of the BL0921. This

low frequency inherently means a long accumulation time between output pulses. The output

frequency is therefore proportional to the average real power. This average real power information

can, in turn, be accumulated (e.g., by a counter) to generate real energy information. Because of its

high output frequency and hence shorter integration time, the CF output is proportional to the

instantaneous real power. This is useful for system calibration purposes that would take place

under steady load conditions.

Offset Effect

The dc offsets come from the input signals and the forepart analog circuitry.

Assume that the input dc offsets on the voltage channel and the current channel are U

offset

and I

offset

,

and PF equals 1 (φ=0).

p

(

t

)

=

[

U

cos(

ω

t

)

+

U

offset

]

×

[

I

cos(

ω

t

+ Φ

)

+

I

offset

]

=

UI

UI

+

I

offset

U

cos(

ω

t

)

+

U

offset

I

cos(

ω

t

)

+

cos( 2

ω

t

)

2

2

Figure 3.

Effect of Offset

As can be seen, for each phase input, if there are simultaneous dc offsets on the voltage channel

and the current channel, these offsets contribute a dc component for the result of multiplication.

That is, the offsets bring the error of U

offset

×

I

offset

to the final average real power. Additionally,

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Total

13 Pages

3/15/2007