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Old 10-07-2015, 01:59 PM   #2146 (permalink)
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Originally Posted by MPaulHolmes View Post
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).
That sounds like reliability could be an issue. TI still has this in product shakedown, right? The bus is proving that the system works in the 'real' world?

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.
Agreed. In our industry, it's the initial acceleration that is important ... and all is good if the controller can command enough torque to do what the control system is asking for. Once the load is up to speed and there are minor changes, or even major changes, you are looking for reproducibility. Maximum acceleration or deceleration is hard on the process.

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.
Cool - a first 'production' sale?

thingstodo: How hard will it be to get the 64 ticks/rev encoder working?
Not hard, I hope. It will likely take more time than I think .. but that's normal.

I think sensored load tests are probably the best way to go for the ACIM for the moment.
OK with me.

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".
I have a tachometer target and sensor for the DC motor. When the AC and DC are coupled, I should have a pulse train .. not sure if it will be 2 pulses per rev, or 4, or some other number. I should be able to get that working (EVTV purchase for my car) but it likely operates at 12V. I'll start with 5V in case the operating range is wide ... and I need to get it operating anyway for my car so I may as well do it now.
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