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RE: Terry's DRSSTC -"different" H-drive functions...

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 02:27 PM 1/12/2005, you wrote:
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

But suppose we instead just turn off the top two IGBTs and turn on the bottom two... No energy is being added now and the H-bridge is still just basically a dead short to the primary so the primary loop current can continue ringing at a relatively low loss. By keeping the bottom two IGBTS on, we basically just let the primary loop "freewheel" and not waist the stored energy as well as reducing the thermal load on the IGBTs!! Of course, running that loop at say 300 amps for a long time will heat the IGBTs too, so that may be a wash...

This is like what H-bridge DC motor drivers do, and essentially, for the same reason. You don't want to try to dissipate the energy stored in the armature inductance, or, for that matter, to try and turn it off, because of the voltage rise.

I wonder if there is a big IGBT motor drive system out there that already does all this? Unfortunately, the late Marc Metlicka was our IGBT motor drive expert... But I don't think any AC motor drive could touch ~200kHz operation... However, there are little motor drive H-bridge (1/2 bridge) ICs out there that can run very fast that might really simply things and they have good current drive to run gate transformers ;-)) They have things like forward reverse, free wheel and break (opposite meaning for our purpose). They also take care of things like cross conduction and all that.

Check Allegro Microsystems http://www.allegromicro.com/ Here's an ap note on three phase motor controllers that drive external FETs

Perhaps one could make a tiny DRSSTC with standard DC H-bridge motor drive ICs right off the shelf!!! They do often have reverse diodes and all that... They have good isolation and protection and could do the above function as a standard feature of those ICs!!

But probabably not the voltage ratings you need. Typically they run up to around 50V and a few amps.