VSC Harmonic Model

[EP007]

I have a VSC, voltage source converter, connected to the power system. The VSC is a PWM inverter. The power supply system fixes the voltage, say 460 V, as well as the frequency 60 Hz. For harmonic studies on the power system, my view is that the VSC should be modeled as a harmonic voltage source, at each harmonic. That is different than a diode bridge rectifier used on VFD's, which are normally represented as current source at each harmonic.

I consider the model to be harmonic voltage sources because of the way that the PWM inverter operates on the fixed DC bus voltage, and also the power grid which constrains the ac voltage magnitude and frequency.

Others, however, view it as harmonic current source representation for harmonic studies.

Does anyone have experience with this?

 

[PHovnanian]

It would probably be best to model this as a Thevenin equivalent consisting of a voltage source plus a series complex impedance for each harmonic. Or a Norton equivalent.

A pure voltage (current) source model will not account for changes in output harmonic content as loading at each frequency changes.

 

[EP007]

The VSC is connected to the grid, which makes the frequency fixed at 60 Hz. There will not be frequency changes in this case.

 

[MAGTiger]

What's the objective of the model? The grid will look like a mainly linear load with some small amount of harmonic current draw, probably negligible. Your PWM inverter should be able to be programmed to eliminate harmonics substantially below the carrier. Meaning no low order harmonics would be produced anyway. A large nonlinear load in close proximity is about the only way you should see harmonics from the inverter. And that isn't caused by inverter. Ideally the inverter would act like any large capacity (low Z) source. Supplying whatever the grid wants.
If you model the inverter as a harmonic voltage source how do you know the magnitude of harmonics to inject?
You will want to model the carrier frequency as a distorted source voltage.

Neil