Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[thingstodo]

What is next for the testing?
- I think I need to save the settings from the run-rotor-test so I can couple the DC motor and do some load tests ... if that's up next.

It would be nice to get the encoder built into the AC motor to work, I guess. I need to find a connector and some pins .. not sure how to source it though.

The Cougar controller was checked out - 0.01 ohms between B- and M-. Dead short. I was going to follow your instructions and cut off the MOSfets until the resistance rises, but would it be easier to hook up a large power supply and just increase the amps until the failed MOSfet .. melts .. burns ... stops conducting electricity? The question I have is whether that will damage anything else.

When you have the code to compare sensorless FOC and encoder-driven FOC done, I can start on that.

[MPaulHolmes]

I'll get a new hex file to you tomorrow. Awesome results!!!

[MPaulHolmes]

What a great idea!!!!! Maybe you could connect the supply to b+ and b- and yhen turn up the amps, measuring the heat of the rightmost leg of all 10 with your finger? Are any of the gate resistors cracked? That is sometimes a clue which one has problems.

[MPaulHolmes]

I would err on the side of the rotor time constant of like 13 even though it isn't the highest RPM. The graph goes up nice and smoothly, then the rpms start to get more erratic. I think that's because the voltage disk is clamping more severely, which means the PI loop is having a hard time commanding the Id,Iq for those larger rotor time constant candidates.

Also, you can do some voltage and current captures (I'll send that today), and find the stator inductance curve, so we can get sensorless moving!

[thingstodo]

Originally Posted by MPaulHolmes

What a great idea!!!!! Maybe you could connect the supply to b+ and b- and yhen turn up the amps, measuring the heat of the rightmost leg of all 10 with your finger? Are any of the gate resistors cracked? That is sometimes a clue which one has problems.

I know that the first one in line, as you look at B+ and B-, has a scorch mark. The damage on that one is pretty obvious. Not sure about the others but I will look at the gate resistors.

Do they crack because they overheat? Getting my finger onto the gate resistor is easier than getting to the correct leg of the MOSfet.

Darn! I wish I could find my infrared gun! I don't use it often, but it is useful when I do. I would also like to start tracking motor temperature as we get into load tests. The AC will be fine for a while with liquid cooling of any sort. I expect that the netgain 9 inch will get toasty if I load it up

[thingstodo]

Originally Posted by MPaulHolmes

I would err on the side of the rotor time constant of like 13 even though it isn't the highest RPM. The graph goes up nice and smoothly, then the rpms start to get more erratic.

From holding the motor (literally, both hands on the motor holding it down on the base) I would suggest that when regen is required to slow down the motor, prior to the next set of values being tested, perhaps slow down the motor a bit more. I don't know what speed things are going, but I got an overspeed fault at max-rpm 6000 ... my testing is done with max-rpm 10000. That's getting up there in the torque curve. We may get better results if the regen drops the motor speed for the start of the test set down closer to 1000 rpm?

I think that's because the voltage disk is clamping more severely, which means the PI loop is having a hard time commanding the Id,Iq for those larger rotor time constant candidates.

That may also be true. The deceleration is more aggressive than the acceleration right now. There is enough torque commanded to lift the 200 lb motor half an inch off the base during regen (which is why I was putting my weight on it to keep my encoder alignment close). The acceleration appears to go hard and then cuts out - not sure if it is current clamp, or you run out of voltage to apply, or your slope on the speed gets too high ... something is limiting the larger rotor time constants.

Also, you can do some voltage and current captures (I'll send that today), and find the stator inductance curve, so we can get sensorless moving!

I'll have an hour or two this evening before we head out to the cabin tonight. If there is anything specific you want me to test (specific currents, or every 10 amps, etc) let me know and I'll get to what I can.

I'm still promising video posted this weekend.

[MPaulHolmes]

That test isn't using regen to slow the motor down. But it would be a good idea. All it's doing is setting IdRef and IqRef to 300, and letting the motor run as fast as it can. Each rotor time constant candidate gets 5 seconds to do its best RPM, and it just starts at whereever the last guy left off. If you got a motor overspeed fault when it was set to 10,000, that means that during one of those 5 second times, the motor got to 10000!, and you evidently didn't get to hear about it because of the fault. holy crap. what voltage/current is this motor rated for? That test is trying to see 44 amps for Id and 44 amps for Iq.

Your motor is much more powerful than mine, and the acceleration is more severe. I think I'm going to include a softer ramp, at least for testing. It will make it easier for things to stay under control.

[thingstodo]

Originally Posted by MPaulHolmes

That test isn't using regen to slow the motor down. But it would be a good idea.

Oh ... so I wonder why the motor goes into regen (I can feel the torque and the bus voltage goes up when the motor is slowing down)

All it's doing is setting IdRef and IqRef to 300, and letting the motor run as fast as it can. Each rotor time constant candidate gets 5 seconds to do its best RPM, and it just starts at whereever the last guy left off.

From what I have observed ... the motor does does not appear to do this. Between 5 second trials, what is the IdRef and IqRef set to? It looks like maybe -52 amps, to me.

I am not seeing the motor current rising to 300. It appears to rise (consistently) to 42 amps per phase with my clamp-on meter. And it stays there with minor fluctuations during the rotor-test, until we get into the regen stuff ... then it swings from +42 amps to -52.5 amps ... what I had described as 'hunting' before.

If you got a motor overspeed fault when it was set to 10,000, that means that during one of those 5 second times, the motor got to 10000!,

I get overspeed faults pretty consistently when I use max-rpm 6000. I have not gotten overspeed faults at max-rpm 10000 as yet.

and you evidently didn't get to hear about it because of the fault. holy crap.

The controller is backing the motor rpm off .. if it's not your code then maybe the encoder is not rated for 10K rpm? I'll have to check! If your code sees goofy speed signals (or the encoder signal goes away when a wire falls off!) from the encoder, it appears to regen ... like when I had the encoder signal running over the motor to get to the controller, that's what I think was happening. Maybe my encoder is limiting the rotor-test results?

what voltage/current is this motor rated for?

I'll take a picture of the nameplate tonight. EVTV lists 300V and 400A. I think I may have posted these numbers backward before, at a higher voltage and lower amps.

That test is trying to see 44 amps for Id and 44 amps for Iq.

That makes more sense. I see 42 with a clamp-on. I'd believe 44.

Your motor is much more powerful than mine, and the acceleration is more severe. I think I'm going to include a softer ramp, at least for testing. It will make it easier for things to stay under control.

Good! Can you add a condition to the start of the test for each group of settings? If you are over 50% of max-rpm, regen until you get down to 20% or 10% so that you have 'room' for the test to run properly?

I think we may be running out of voltage to apply before the test is complete. Would it make sense to flag each of those tests so we don't use the settings .. since they may be warped or at least not optimal? Perhaps log a warning to the terminal with the voltage, current and speed?

Would it make sense to log an error or warning when the encoder signal jumps? Like we are running at 6K and the next update it seems like the motor is now spinning at 4K? or 8K? You will likely need something like this to track encoder versus Sensorless speed when we get to that part.

... I have such good ideas when I don't have to implement the code!

[e*clipse]

thingstodo -

I'd like to thank you for providing that example and reminder of why shielded analog inputs are important. Sometimes it's a bit too easy to think "aww, that's not that important - it's just a matter of a few mV...."

On another note, I was reading a paper about taking measurements of motor parameters to make the control programs work better:
http://cache.freescale.com/files/mic...ote/AN4680.pdf

They mentioned an RLC tester to measure the motor inductance and very low resistances. Damn! You can measure that?? That tool must cost a lot...
Here's a nice used one - for only $37,950!
Agilent 4294A 40 Hz to 110 MHz Precision Impedance Analyzer w Fresh Calibration | eBay

But seriously, you can buy fairly nice hand-held ones from BK Precision:
Model 878B, 40,000 Count Dual Display Handheld LCR Meters - B&K Precision

Have you used anything like this at work? If so, any suggestions for what to look for in a good, affordable one?

Thanks a bunch,
E*clipse

[thingstodo]

Originally Posted by e*clipse

I'd like to thank you for providing that example and reminder of why shielded analog inputs are important. Sometimes it's a bit too easy to think "aww, that's not that important - it's just a matter of a few mV...."

No problem ... I have a bad habit of using what is at hand instead of what I should be using.

On another note, I was reading a paper about taking measurements of motor parameters to make the control programs work better:
http://cache.freescale.com/files/mic...ote/AN4680.pdf

They mentioned an RLC tester to measure the motor inductance and very low resistances. Damn! You can measure that?? That tool must cost a lot...
Here's a nice used one - for only $37,950!
Agilent 4294A 40 Hz to 110 MHz Precision Impedance Analyzer w Fresh Calibration | eBay

But seriously, you can buy fairly nice hand-held ones from BK Precision:
Model 878B, 40,000 Count Dual Display Handheld LCR Meters - B&K Precision

We use a megger on motors to see if there are ground faults, resistance line to line to see if the phases are balanced - if the phases are shorted part-way through the resistance won't match ... that's about it. Once or twice we've checked insulation with a hi-pot. Sorry for the jargon - I can look up the *REAL* names of the instruments if you like

To measure small resistance on large motors we use a ducter. It is an ohm-meter that uses higher current to measure small resistance. 1 amps or 10 amps. The probes are sharp and there are two for + and two for -, so you get a reading on 'corrosion' as well.

The vendor that we use to rewind our motors uses this RLC type of equipment as well as partial-discharge .. a method of measuring insulation breakdown.

As I mentioned - our industrial controllers do their own tuning. It's a 5 minute process when we change a motor to tune to the new motor and away it goes. It just means I have to drive to site some evenings and weekends when motors fail in production ...

Have you used anything like this at work? If so, any suggestions for what to look for in a good, affordable one?

Nope