VFD Model for Harmonic Analysis
VFD Model for Harmonic Analysis
(OP)
For harmonic analysis on industrial power systems, I normally see the VFD's represented by current harmonics, for ac induction motor applications, and pulses of 6,12,18, etc. Now I see a report that represented the VFD's by voltage harmonics. The software is not an issue as it can accept both. My concern is that this may not be the correct method, which then affects decisions. My question is: Does anyone know of any reasons or situations where that approach could be used?






RE: VFD Model for Harmonic Analysis
It's hard to give a more specific answer without knowing the software being used and the purpose of the modeling.
David Castor
www.cvoes.com
RE: VFD Model for Harmonic Analysis
They have not done that. They have represented the VFD by non-linear voltage in the form of harmonic voltage spectrum. It still results in calculated harmonic currents and voltages in the system. However, I can't see how a VFD can be modeled that way, since the harmonic voltages at the VFD terminal are dependent on the network inpedance and other factors, and to represent them as constant does not seem correct. Also, how can anyone know what the harmonic voltage spectrum of a VFD is?
The purpose of the modeling is to assess the harmonic currents and voltages in the power system network.
RE: VFD Model for Harmonic Analysis
I also don't see how you can represent the VFD as a fixed voltage harmonic model since the voltage harmonics vary with each power system.
My first guess would be the report you saw bypassed the part where the current harmonics are modelled to produce the voltage harmonics. It almost sounds like whoever generated the report just plugged in some arbitrary or "field proven" voltage harmonic levels and looked at their effects on various components in the power system.
RE: VFD Model for Harmonic Analysis
RE: VFD Model for Harmonic Analysis
1) not all modern VFDs have filters, and
2) even the ones with filters will still produce some harmonics (just not as badly as if they didn't have the filter).