open nuetral, u got it. same phenomenon as our ham radio SWR on xmission lines.
....
each newer generation vfd seems to get faster and faster turn on/off times of the IGBTs.
There's a solid reason for that, that many but not all here will surely grok. Switch transistors have 3 operating regions:
If off, the voltage across it is high, the current is zero, so watts dissipated is ~zero
If on, the voltage drop is low, the current is high, so watts is not as low as zero but...
If partially on, the voltage drop is medium, the current is too, and the power is *%^&*...until the smoke escapes.
So you want to get that IGBT or FET through the linear region ASAP.... or else. To that end, on the electric car three of use are building, we actually have multiple stages of gate drive for the FETS. We're getting bigger FETS and may need ZXGD3004E6TA's driving the Si8233 we now use by themselves. We're talking gates pulses in the amps {not micro or milli regions....} to get there.
Of course, those transitions then make other problems including RFI.... But our motor control leads are only a few feet long...
Jrafe:
I did understand it was a SWR issue but that's insufficient help to me re: fully comprehending why it's trouble in this case, at least without too much thinking to be fun...I'd think convention L-C filtering of the output would resolve things.