In an AC/DC-AC (DC Link) with TRU 12 pulse diode, dc link and a controlled 12 pulse IGBT inverter, the power factor at the generator terminals decreases about 2% if the generator output voltage steps from 300Hz to 400Hz. Why does it happen?
Inductive reactance is propotional to frequency. Higher the frequency means higher inductive reactance. Higher inductive reactance higher the reactive power Q [VAr] in total power S [VA] = P+jQ.
Power factor is P/S. decreases if there is an increase in S due to an increase in Q.
Assuming your P is constant, your Q is definitely getting higher somewhere to make power factor decline. Your Q is dependent on frequency so higher frequency caused your Q go higher.
Although you have a dc link, but it is still reasonable to have a decrease in the power factor as f increases. This is due to the increase of the reactances every where which leads to more shift between the current and the voltage. Consequently the PF decreases.
Increasing of frequency leads to increasing of reactive component of power so power factor decreases (via increasing of angle between active power P and apparent power S).
Thank you all for the comments.
It is true that the PF at generator terminals drops much more when I add reactive loads at the inverter output, even with the DC Link.
Well, but this power factor is not so easy to correct. It seems not work with a bank of capacitors. How could I mitigate the degradation of PF?
I forgot to say that I am using PI controller for the field excitation of the AC synchronous generator. It keeps 330Vdc in the DC Link. I have noticed that the voltage at the generator terminals increases few voltages for each step of frequency. This could contribute to PF drop?
PF=P/S; with P=(VgVc)sin(delta)/X. Where, Vg is the voltage terminal to the generator, Vc is the voltage terminal to the converter, X is the line reactance between generator - converter, and (delta) is the voltage phase difference. Delta is a function of frequency which can be controller through the PWM of converter. Varying the frequency of the control signal of the PWM implies change in P and PF.
I got also similar problem but in my case I have an inverter with LC filter. we step up the fundamental frequency from 60Hz to 400Hz for sure the reactive power increase but my main concern is why the voltage across the capacitor filter increase as well while the input voltage is constant. Simulation illustrate the issue. Left is the load voltage and current and right is the inverter output voltage and current.
why the voltage increased?
This occurs due to presence of harmonic currents and also improper wiring.
As frequency increases increase of reactive component of power and power factor decreases.
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