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

[Piotrsko]

Based on what I observe over on some of the other power forums I stalk, you have probably fried the power transistors and probably also the drivers.

Isn't there some snubber diode across the igbt to sink the back emf?

From what I recall igbt failure mode is generally shorted on. Theory says the gate becomes damaged.

My experience is that it doesn't take long to crispy the weakest part reverse biased.

I believe if you powered up the controls with 12v, and spun the encoder/ motor by hand, an ohmmeter could be used accross the phases and battery ground to show a decrease in resistance when the thing switch on. I am guessing you already checked that you were getting switched voltages on any pair of motor leads. This is where a scope would be handy, but I have done it with a analog simpson set to whatever the battery pack max is.

[MPaulHolmes]

These IGBTs have the diodes inside from emitter to collector for each IGBT. There was not a continuous massive amount of current when B+ and B- were reversed, so that makes me think maybe they gracefully failed opened? There are several little thin wires (like 28 awg or something) inside the IGBTs that are floating in a gel, which connect to the collector and to the emitter tabs. I think they are designed to act as fuses. I would be interested in seeing the inside of the IGBTs. They have tiny screws in them, and then the little plastic top can pop right off, or you might need to bend the metal tabs first for the plastic top to be removed. My guess is that some of those little thin wires have failed opened, but I don't know for sure.

[thingstodo]

Originally Posted by MPaulHolmes

These IGBTs have the diodes inside from emitter to collector for each IGBT. There was not a continuous massive amount of current when B+ and B- were reversed, so that makes me think maybe they gracefully failed opened? There are several little thin wires (like 28 awg or something) inside the IGBTs that are floating in a gel, which connect to the collector and to the emitter tabs. I think they are designed to act as fuses. I would be interested in seeing the inside of the IGBTs. They have tiny screws in them, and then the little plastic top can pop right off, or you might need to bend the metal tabs first for the plastic top to be removed. My guess is that some of those little thin wires have failed opened, but I don't know for sure.

The weather is nice, and projects are calling ... this post-mortem may not get done until it's cold outside.

Even though I *REALLY* want to know what failed!

[wootwootman]

I was able to get everything wired and powered up, so I got some testing done yesterday evening for results to analyze this morning. I started with kp=5000 ki=100, then moved on to kp=10,000 ki=200 and went back to kp=3000 ki=50. I collected the data and tried the different K values before plotting it, so at the time I wasn't aware I should try higher values. I'll try kp=15000, 20000, 25000, etc later today

I did notice that 'run-pi-test2' would take a few tries to get usable data; often it would only return slight dips or a near-constant flat line. These plots are made from an average (6-9 runs out of ~20 for each setting) of the usable data for its respectable setting

[MPaulHolmes]

what motor do you have again wootwootman? And what voltage are you running this test at?

[wootwootman]

Originally Posted by MPaulHolmes

what motor do you have again wootwootman? And what voltage are you running this test at?

It's a 2013 Leaf motor with a 13S Lipo (48V nominal, 54.6V peak) pack made from C-Max cells. I'm planning on eventually using the rest of the cells in my pack to bring the total to 38S (140.6V nominal, 159.6V peak)

Along with changing kp, I've also noticed a difference in changing the kp/ki ratio. In the attached pic, four usable results were averaged for ki=400 and six for ki=322. It seems going from the suggested ~60 (ki=322) to 50 (ki=400) works faster. I'll stick with this ratio and keep raising kp

EDIT: Added some kp=30,000 results. Wondering what the deal is with the occasional undershoot, it might've effected my previous average plots. Or are those undershoot-ing results the ones I'm supposed to be looking for?

[MPaulHolmes]

It's OK to err on the side of gentler convergence rather than most harsh convergence. Any undershoot means that it's too aggressive, and the Kp and Ki should be reduced some.

[thingstodo]

Originally Posted by wootwootman

I did notice that 'run-pi-test2' would take a few tries to get usable data; often it would only return slight dips or a near-constant flat line. These plots are made from an average (6-9 runs out of ~20 for each setting) of the usable data for its respectable setting

a few tries ... I only ever did one at a time for each set. Before I rip apart my setup, to get my garage back, I'll likely give'er one more try. I don't expect it to work, but it's worth a couple of hours.

[MPaulHolmes]

I've only had to do it once too. Could there be a loose connection anywhere?

[thingstodo]

Originally Posted by MPaulHolmes

I've only had to do it once too. Could there be a loose connection anywhere?

So once should be enough? That makes more sense ...