[SOLVED] fixed power factor inverter control

[danilorj]

Hey guys

do you have any block diagram control, or know some reference, so I can control a single-phase inverter to operate at fixed power factor?

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[kappa_am]

what is your application?
you need a PLL that its output follows voltage angle and a Park transform. then determine Iq (which is perpendicular to voltage vector) amplitude according to your demanded power factor. all can be implemented by software in DSP or MCU.

Good Luck

 

[danilorj]

Could you, please, give me more details of this control strategy?

 

[danilorj]

it is for a fuel cell application.

 

[kappa_am]

your inverter is connected to grid. so you need phase angle of the grid voltage. obtain it with any convenient method. suppose the angle of current is measured referenced to angle of voltage vector. decompose current vector in a frame in which voltage vector is x-axis, and an axis perpendicular to voltage vector . As you know in-phase current (id) generates active power and perpendicular current (iq) generates reactive power. control id and iq according to demanded active power and reactive power respectively. now obtain angle and amplitude of current by using id and iq. use hysteresis band modulation or any convenient method to generate this current at output of the inverter.

Good Luck

 

[danilorj]

Is this what you mean?

 

[kappa_am]

I mean something like this. I sketch it for single phase system. 3-phase system is something alike.

 

[danilorj]

This blank square in part (4), I assume it is the inverse park transformation, isn't it?

 

[kappa_am]

a similar thing.
you have iq and ip so you have amplitude of vector i
|i|=sqrt(iq^2+ip^2)
and you have angle of the vector i
so you can construct vector i.

 

[danilorj]

One more thing... This |Vg|, you mean the RMS of Vg?

 

[kappa_am]

No, in RMS value you loose data, because you have Mean in formula. It's magnitude of vector Vg.