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Relationship between PF and THD

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biswaIITH

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Are PF and THD directly related in PFC circuit???If i am getting a THD of 11%,does that mean that its true Power factor is .994 by the formula PF=1/sqrt(1+sqr(THD))...
 

dick_freebird

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I don't think so - PF is the time relation of voltage and
current. THD is going to arise from the nonlinear elements
(e.g. diode bridge, active switches) in your PFC circuit
"doing their thing" in a not-smooth-L-C way. I suppose
at different power factors the nuances of harmonic
generation might change some, but this is about the
operating behaviors of the nonlinear elements still.
 

FvM

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Yes, there's a direct relation. But total power factor is the product of displacement power factor (cos phi) and distortion power factor. In case you know that cos phi is unity (no reactive power) you can convert THD to PF, as calculated in your example.

All calculations here https://en.wikipedia.org/wiki/Power_factor
 

SunnySkyguy

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Correlation only exists for a known equivalent circuit.
Linear (RLC) will be quite different from non-linear ( pulsed current at a particular phase offset) and then amount of filtering affects THD.
 

biswaIITH

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Yes, there's a direct relation. But total power factor is the product of displacement power factor (cos phi) and distortion power factor. In case you know that cos phi is unity (no reactive power) you can convert THD to PF, as calculated in your example.

All calculations here https://en.wikipedia.org/wiki/Power_factor

Displacement powerfactor is cosine of the angle between the supply voltage and the supply current.For my application how to find out that???In the CRO,i am getting the supply current but i cant use the angle between the supply current and the supply voltage to find the displacement powerfactor.
 

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Dsiplacement angle must be determined for the fundamental wave. For a low THD like 11% the phase shift of zero crossings should give a roughly correct number. It can be of course determined with an oscilloscope.
 

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