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I was actually switching at 10KHz. The good news at least on my end so far is, this layout hasn't had any problems in the DC case, and that's been with current up to 1550amp at maybe 160v. The controllers are identical except that in one case, it's 3 sine waves being formed, and in the other case it's either a constant frequency PWM or variable frequency PWM (to make the rushing water sound rather than a piercing noise). I had set the DC controller's PWM frequency to like 4KHz at one point (on accident), and it was making some of his instrumentation go bonkers. When it was changed to 10KHz (and 9-12kHz in the spread spectrum case), that problem went away.
It may help that the control stuff is several inches away from the high power switching, and the face of the high power switching is a copper sheet rather than a cable. There's almost no loop area between the copper sheets. The sides where the radiation can leak out is small and far from the bulk of the control board. It will be very interesting to see how things go at higher voltage and current. I've only tested it at 20 amps and maybe 120 volts. I hope the results are similar to the DC controller, as the layouts are the same.
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