commutation

[seayaker]

I built a generator that I need to commutate, that is the polarity must switch every 22.5 deg. of rotation. An H-Bridge circuit will work if I can find the right components. The output will be up to 100v 50a, it will have to switch at at least 80 hertz. Any suggestions?

 

[duffy]

You would need a chopper wheel with 8 flags in it, an interruptor-style opto to read the flags, an NPN or two to give a signal and a complementary signal, 4 push-pull gate drivers to run the bridge, 2 p-channel and 2 n-channel MOSFETS rated for over 100V and 50A for the bridge itself.

Shouldn't be terribly difficult, but there's going to be a little technique involved. The mosfet drivers are not going to operate at 100V (which I assume is the maximum generator voltage) so you are going to have to give them both a positive linear pass regulator that's about 15V above ground, and a negative regulator that's always 15V below the positive rail from the generator, both of which can withstand 100V. The saving grace is that the average current is very small (though the peak gate current could be an amp). Both the opto signal and it's complement are going to have to be referenced and limited to each rail and regulator so you don't damage the input to the MOSFET driver chips.

Strange request, mind if I ask what you're building?

 

[seayaker]

thanks for responding

A generator for wind, hydro, ect. I designed a different kind of stator and for the prototype I thought a single phase generator would be easier to work with.

 

[duffy]

But this setup will change frequency with speed!

I think maybe you didn't state the problem correctly. I think maybe you have an alternator, and want to do synchronous rectification or something...?