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

MPaulHolmes · 10-07-2015, 07:13 AM

As for sensorless, I'm fairly sure, based on what I've tried, that getting it to work is like balancing a ball on the top of a hill. I think that if you don't have the motor's stator resistance and inductance fully characterized over the range of RPM and temperature and load, you will still get a "rotor flux angle", but it will slowly drift away from the true angle, and after a short time you won't be commanding current in the right direction. TI is doing 20kHz 12 bit precision A/D conversions on all of the 3 motor currents AND all 3 motor voltages, AND constantly checking the stator resistance while the motor is running, and knows the stator inductance at every rpm in order for it to be used in a test vehicle (a bus. maybe there are others now).

I think that with the hardware I'm using, I could fully characterize stator resistance and inductance, and then get it to ramp up relatively slowly, and maintain a relatively constant RPM, but I have my doubts about using it in a car. I think you have to be hyper-vigilant, babysitting the motor's constants on a moment by moment basis to get it to work under the conditions of normal daily driving. That's a very different application from a sensorless AC motor in industry. I think that to give this the best chance it could have I would have to change the control board hardware. I still would like to get it to work, but maybe we should stick with encoder/resolver approaches for cars for now.

A guy in india wants to use the controller for some rickshaws, and I have to get a board he ordered shipped out to him in just a few days, so for the next few days I'm going to just try to get it to a place that will autotune and be ready to run as easily as possible. I had been hoping to get the sensorless working before that deadline, but it's not going to happen in 3 days.

thingstodo: How hard will it be to get the 64 ticks/rev encoder working? I think sensored load tests are probably the best way to go for the ACIM for the moment.

I really want to get eclipse's motor/resolver board tested and working too.

If a hall sensor was added to the motor post cheaply, a single pulse per revolution should be enough for sensorless to work. You could do a hybrid of sensorless and sensored FOC. I should try that. I think you just epoxy a small magnet to the shaft, and add a hall sensor or 2 as a cheap "encoder".

10-07-2015, 07:13 AM	#2145 (permalink)
MPaulHolmes PaulH Join Date: Feb 2008 Location: Maricopa, AZ (sort of. Actually outside of town) Posts: 3,832 Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000 Thanks: 1,368 Thanked 1,202 Times in 765 Posts	As for sensorless, I'm fairly sure, based on what I've tried, that getting it to work is like balancing a ball on the top of a hill. I think that if you don't have the motor's stator resistance and inductance fully characterized over the range of RPM and temperature and load, you will still get a "rotor flux angle", but it will slowly drift away from the true angle, and after a short time you won't be commanding current in the right direction. TI is doing 20kHz 12 bit precision A/D conversions on all of the 3 motor currents AND all 3 motor voltages, AND constantly checking the stator resistance while the motor is running, and knows the stator inductance at every rpm in order for it to be used in a test vehicle (a bus. maybe there are others now). I think that with the hardware I'm using, I could fully characterize stator resistance and inductance, and then get it to ramp up relatively slowly, and maintain a relatively constant RPM, but I have my doubts about using it in a car. I think you have to be hyper-vigilant, babysitting the motor's constants on a moment by moment basis to get it to work under the conditions of normal daily driving. That's a very different application from a sensorless AC motor in industry. I think that to give this the best chance it could have I would have to change the control board hardware. I still would like to get it to work, but maybe we should stick with encoder/resolver approaches for cars for now. A guy in india wants to use the controller for some rickshaws, and I have to get a board he ordered shipped out to him in just a few days, so for the next few days I'm going to just try to get it to a place that will autotune and be ready to run as easily as possible. I had been hoping to get the sensorless working before that deadline, but it's not going to happen in 3 days. thingstodo: How hard will it be to get the 64 ticks/rev encoder working? I think sensored load tests are probably the best way to go for the ACIM for the moment. I really want to get eclipse's motor/resolver board tested and working too. If a hall sensor was added to the motor post cheaply, a single pulse per revolution should be enough for sensorless to work. You could do a hybrid of sensorless and sensored FOC. I should try that. I think you just epoxy a small magnet to the shaft, and add a hall sensor or 2 as a cheap "encoder". __________________ kits and boards Last edited by MPaulHolmes; 10-07-2015 at 10:47 AM..