Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

Automcdonough · 07-27-2010, 09:56 PM

looks like I'm not too late to this party. I'm an EE with experience making DC-DC converters and rectifiers.. mostly in the 300W~2kW range.. 360VDC input side.
I just now came across this in my quest to DIY a motor driver.. I might have had some circuits to toss at you for the DC version but I'd rather concentrate on this as I'm on a mission for AC.

Most of what I did was analog power, none of our stuff used microcontrollers because they are too slow for a safe short-circuit current limit, and too slow for stable control loop when the system runs at 100KHz.

My approach might be overkill considering we're going to be at 1/10 the frequency, the micro can probably keep up with things. I wanted the micro to output four 0~5V analogs down to the power board. First 3 are PWM duty cycle for each leg, 4th is current limit setpoint. Could also be sent as digital w/ analog conversion being done on power circuit.

On the power board would be 3 PWM drivers or one of those IR control chips with a 100% analog current limit that operates independent of the micro (would use setpoint or hardwired max, whichever is lower). Motor speed, current of each leg, bus voltage, bus current, temperature, etc all would be conveyed back up to the micro. Power board would also contain shoot-thru protection and some other un****withable circuits, as well as micro controllable ones like undervoltage lockout, overvoltage lockout, overtemperature derate/shutdown.. all with hardware maximums that should hit if the micro goes on holiday. For the most part the analog circuits will be cheap and simple, hopefully avoiding expensive LEM's and whatnot. Compared to what I'm used to this low-frequency high-inductance circuit should be cake.

I have a good feel for what to do with all this but when it comes to AC motor theory and choosing+programming the micro itself I'm pretty weak.

Also I should mention that I intend to drive 480V motors, DC bus will tolerate at least 800V. I was considering breaking that boost/buck front-end for the battery into a separate box which would watchdog the batteries carefully, mostly because I wanted to use 4 motor drivers (electronic throttle control..)

07-27-2010, 09:56 PM	#276 (permalink)
Automcdonough EcoModding Lurker Join Date: Jul 2010 Location: Cleveland, OH Posts: 89 Thanks: 5 Thanked 7 Times in 5 Posts	looks like I'm not too late to this party. I'm an EE with experience making DC-DC converters and rectifiers.. mostly in the 300W~2kW range.. 360VDC input side. I just now came across this in my quest to DIY a motor driver.. I might have had some circuits to toss at you for the DC version but I'd rather concentrate on this as I'm on a mission for AC. Most of what I did was analog power, none of our stuff used microcontrollers because they are too slow for a safe short-circuit current limit, and too slow for stable control loop when the system runs at 100KHz. My approach might be overkill considering we're going to be at 1/10 the frequency, the micro can probably keep up with things. I wanted the micro to output four 0~5V analogs down to the power board. First 3 are PWM duty cycle for each leg, 4th is current limit setpoint. Could also be sent as digital w/ analog conversion being done on power circuit. On the power board would be 3 PWM drivers or one of those IR control chips with a 100% analog current limit that operates independent of the micro (would use setpoint or hardwired max, whichever is lower). Motor speed, current of each leg, bus voltage, bus current, temperature, etc all would be conveyed back up to the micro. Power board would also contain shoot-thru protection and some other un****withable circuits, as well as micro controllable ones like undervoltage lockout, overvoltage lockout, overtemperature derate/shutdown.. all with hardware maximums that should hit if the micro goes on holiday. For the most part the analog circuits will be cheap and simple, hopefully avoiding expensive LEM's and whatnot. Compared to what I'm used to this low-frequency high-inductance circuit should be cake. I have a good feel for what to do with all this but when it comes to AC motor theory and choosing+programming the micro itself I'm pretty weak. Also I should mention that I intend to drive 480V motors, DC bus will tolerate at least 800V. I was considering breaking that boost/buck front-end for the battery into a separate box which would watchdog the batteries carefully, mostly because I wanted to use 4 motor drivers (electronic throttle control..)