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Re: Good Deal? SURE !! (three phase inverter)
> The hard part will be getting the 3 sine wave signals 120 degrees out of
> phase. The easy but expensive way to do this is to program 3 eproms with an
> 8bit sine wave then scan throught the addresses with scaled decade counters
> 120 degrees out of phase and feed the outputs to 3 8bit D/As.
>
Even more elegant and much cheaper, use the 6 bits out of the eprom to
drive the H bridge components directly. Encode the PWM waveform in the
eprom and step through it really fast. Say you want a switching rate of
25.6 kHz, and you want to generate 50 Hz sine waves. The eprom only
needs to be 512 steps long..
International Rectifier has a part that is designed to drive 6 IGBT's
and, whats most important, a free eval board for the part. All you need
to do is supply the digital drive to the chip and it does the level
shifting, etc.
Of course, such a device will probably have terrible regulation, and so
forth, but, it'll work, and you have a variac to adjust the voltage
anyway.