Overcurrent trips at low speed

[manny]

As my E saxo project is nearing completion. I am doing some test drives. It drives pretty good.

Saxo Project:
viewtopic.php?t=4837

Volvo V60 motor:
viewtopic.php?t=3859

Volvo XC90 inverter:
viewtopic.php?t=3675

But when pulling away from a standstill sometime the inverter trips with a overcurrent error. If I get some speed than I can floor the pedal without a problem.

Have played with the iqkp and idkp values did not make a notable difference. With the handbrake on the Iq and Id are nice and stable.

With this being a OI board I made myself it could be loads of different problems.

Would like some comments on things to check/try before I remove the inverter to scope the current sensors to check the signal for noise or something. And check the reference voltages for the overcurrent protection circuit.

Any help is greatly appreciated.

[P.S.Mangelsdorf]

Is this occurring with low throttle input or high throttle input?

On the Tesla LDU, we had lots of issues with low speed, low throttle which were solved by the introduction of fweakstrt, which is a higher value of fweak for low speed, low throttle. But that's on the sine firmware, I have no idea how to apply that info to the FOC firmware.

[johu]

First I would lower throtramp. Between 3 and 10. Gives the PI loops more time to settle. Make regenramp < 1

You can also try lowering curki.

That's pretty much all you can play with.

Does it actually OVERCURRENT trip or is it some fault signal from the gate driver? The latter could be from over temperature. When the inverter is conducting pretty much DC without handing off current from one leg to the next, the "most active" IGBT at a given motor angle heats up faster

[manny]

Is this occurring with low throttle input or high throttle input?

Mosty with high throttle, but it also happened when carefully backing out of the garage.

First I would lower throtramp. Between 3 and 10. Gives the PI loops more time to settle. Make regenramp < 1

You can also try lowering curki.

Lowering throtramp did not do much. Lowering curki made it better.

Took the inverter apart to check the voltages at the ocurlim comparator.

• current sensors output 2.5V at 0A
• current sensors scaled 1.47V
• low threshold 0.587V
• high threshold 2.352V

• Delta low 0.883V
• Delta high 0.882V

So 0.882 /3.3 = 0.267 x 4095 / 2.4375(il1gain) = 449A
That is doing exactly what is should

When going through the schematic I found the reason why the udc whas stuck at 398V. thought is whas the limit from the inverter. Dumb in hindsight . With udcgain 10.28 @ 420V = 4317 digits, the input the adc input is overloaded. So I added a resistor to make a voltage divider with the 10k resistor in the input filter. Have seen overloaded inputs affect other adc inputs on microcontrollers. but it is not that much.

When taking the inverter apart I found out that my contactors are welded shut. So not able to plug that back in.
need to fix that first to continue testing. Maybe I can rig up a power supply to check the current sensor signal with the scope.

[manny]

So took the inverter apart. Luckily I did not need to drain the cooling system.

There seems to be quite a lot of switch ringing on the current waveform. 150mV equates to 45A

measurement setup

Red: current sensor signal Yellow: is ch3 PWM (for timing)

Overview

zoomed in

after voltage divider

Have tried adding a capacitor before the voltage divider/input filter (as on the first picture). That didn't do much.

Thinking about adding a chip bead ferrite inline. Need to find one with that works on the 26MHz most are 100MHz or higher

Don't think that I can do something about the origin of the noise.