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Old 06-09-2010, 12:18 PM
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jhuebner jhuebner is offline
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Default Another homebrew AC-controller

Hello everybody!

I have been reading here for a while and I'm simply impressed by the projects shown here.

So today I want to make my first humble contribution.

Short story:
1,5 years ago I came up with the idea of converting a regular ICE car electric (how unusual ). I decided it would have to be an AC-motor since most of the complicated parts of spinning it are done in software plus it offers the best effiency. I also found out that standard ACIMs are really cheap and can be overpowered for short periods. Unfortunatly I also found out that controllers are really expensive.
Being an electrical engineer I decided to give it a try. My first inverter consisted of some BUZ50 mosfets and controlling circuitry around it. It basically worked but of course would only drive a 1:10 model of a car
So I scaled up and have now got this:

It uses a 1200V 90A IGBT, IGBT drivers, a hardware PWM-module and a PC. It basically spins the motor at whichever frequency you set it to and it even uses the space-vector modulation scheme to achieve the highest possible amplitude. I know 90A isn't much but it's a start.

At the top you see the voltage with the little space vector "dent" and the current at the bottom.

There is one problem though: it is all open loop and it uses a PC. Also the PWM resolution is just 8 bits.
My plan is to put the controller program on a little C which offers 16-bit pwms. For closing the control loop I want to start out with a speed sensor and thereby control the slip of the ACIM in some clever way that is still to be figured out. Since I have never seen any serious motor controller without current sensors and vector control I might have to implement that as well. There are closed loop sensors already on the IGBT-module but their output somehow didn't seem to linearly follow the amplitude of the current.
When all is finished I want to document it like the well known Open Source Motor Controller.

So... do you think this is a promising project worth continuing? And if yes, any suggestions?

Looking forward for replies
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