phase converters for big iron

Simon> All, On 4/28/05, Paul Koning <pkoning at equallogic.com> wrote: >> Simon> [...] Simon> All the solid state phase converters I have come across use a Simon> three phase H bridge to generate three phases from a common Simon> intermediate DC rail. The incoming voltage is converted to DC, Simon> switched, PWM synthesising a sinusoidal at the required Simon> frequency. Simon> The PWM works pretty well for induction motors. I would expect Simon> big iron to have some issues. Simon> Two areas of initial concern. Simon> 1) Transformers in linear supplies seem to be very well suited Simon> for 50/60Hz. Trying to feed them with a square wave with Simon> frequencies of up to 30KHz + would probably not do them a lot Simon> of good. They may be able to handle it just fine, but then Simon> again they might not. Yes, but do solid state converters put out square waves, or rounded waves? I'd expect the latter, or certainly nothing with realy fast rise times. Don't those things ofen use IGBTs? Those don't switch all that fast as I understand it. In any case, I don't see why a transformer would be any less happy about harmonics than a motor; they are both windings on laminated cores. Also, square waves have theoretical spectra out to infinity, but the amount of energy above a few kHz for a 60 Hz fundamental is very low. I don't have the Fourier transform memorized, so I can't be more specific... paul