Issue with V/F-FOC transition screeching and stopping

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User17346
Level 2
Level 2
10 replies posted 5 replies posted 5 questions asked
Hi all,

I have my motor running under V/F. It runs with a very high current, and so gets a bit hot, but it is fundamentally running, which means the PWM, SVM, wiring, programming...etc... is working. The current waveforms comming out of the opamps and into the chip look pretty good. Credible, square pulses.

The issue is that when it reaches the end of the V/F ramp up, or if I try starting in FOC mode, it goes screeeeegreeeeecreeeeeeee and loses synch.

The current through the FETs becomes very high, tripping the current limit on my PSU, and has burnt a 16A MOSFET. Now replaced and spinning again under V/F.

I am using a custom board (see pics) with XMC4100 64 pin 128k. I have PWM U,V,W allocated to CCU8 on P0.5,4,3 and ADC U,V,W on 14.5,4,3 respectively. The Us Vs and Ws for the ADC/PWM match up on my board.

Currently bolted to a motor with a fan load, which I can actually keep at my desk... going in something else eventually.

Changing the parameters doesn;t seem to obviously help. I can get it to swap to FOC at a higher speed, but no help.

Using Dave Version: 4.4.2. PMSM FOC library 4.2.12

Any help much appreciated.

https://youtu.be/GFgws0zCkco


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3927.attach
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User17346
Level 2
Level 2
10 replies posted 5 replies posted 5 questions asked
Turns out the issue was that the opamp I was using suffered from occasional phase inversion, on the negative current readings. This was only very occasional - maybe once in every 100PWM cycles, which made it hard to see on the 'scope. Opamp was rated for rail:rail operation, but it turns out that was only for the output.

Replacing with a better/more appropriate opamp solved the issue, and I now have (mainly) good FOC on my motor. Some issues with overloading it until it loses synch and it not realizing it's lost synch, but this is probably fixable with the current limitation/trap.

Overall, quite happy with this chip/setup, it worked pretty much first time once I'd corrected the opamp issue, and the MCU itself survived my previous idiocy with connecting the VDDC pins to 3.3V...
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