[cpate]

Hey guys, for the past few months I have been putting together an Open Revolt controller with a VLA500 IGBT driver and 3 Fuji 2MBI300L-060 IGBTs. I've read about a few other people doing the same thing and I've read the documentation on driving IGBTs and minimizing inductance. However it seems that I've done something wrong because today we tested the controller and 2 or 3 of the IGBTs blew. We first tested it with no load or battery hooked up, just to test the IGBT driver. The signal looked fine, with the low Base-emitter signal being -8v, and the high being 16v. We then hooked it up to a 12v battery and a 30-ohm burner, and it ramped the current up and down just fine from 0 to .5 amps. I did not notice anything weird about the gate drive signal on my oscilloscope. Then we hooked up our 144v traction pack and when we opened the throttle up, a high whine and then a pop was heard, and current went up to about 7 amps through the burner.

Here are some pictures if anyone can spot any stupid mistakes I might have made. The gate resistor on each IGBT is 5.6 ohms, as per the IGBT spec sheet. Unfortunately, I didn't bother to implement any voltage clamping diodes on the gate wires. Could that have been my mistake?






Any advice or comments are appreciated! Thanks!

[z_power]

This might be not very important but shouldn't be the current sensor on M- busbar? Looking at pictures it's on B-, please correct me if I'm wrong. It doesn't sense current flowing trough freewheeling diode (E1->C1) during switchoff phase of PWM.

edit: it's hard to see, are E1-G1 connected on each module? are gate resistors parallel to g-e?

[cpate]

Thanks for the response!
Maybe you are right. I just assumed that the current sensor is supposed to measure battery current.
As for the resistors, there is a 10k ohm resistor between E1 and G1 and another one between E2 and G2 on each module. The 5.6 ohm gate resistors are between the driver and G2 on each module. The E2's are all connected to the driver.

[bjfreeman]

Originally Posted by cpate

Unfortunately, I didn't bother to implement any voltage clamping diodes on the gate wires. Could that have been my mistake?
Any advice or comments are appreciated! Thanks!

can't find a spec sheet but if you don't have FWD across the Source and Drain of each, the inductive EMF will be many time 144 volts. I am guessing about 1,440 volts.

Wire dressing to keep inductive pick up.

[subcooledheatpump]

Across the gate wires? wouldn't adding a diode create a short circuit during negative gate turn off? I think he is using the FWD of the upper IGBT across C1 and C2E1

By the way, what switching frequency are you running those at?

I've got the same IGBTs, I use them for a low frequency induction heater, I don't run them above 10 kHz.

Also with those crazy gate connections you've got going on, I would recommend increasing the Rg (gate resistor) to about 10 ohms. You'll get alot of voltage buildup between the gate driver board and the IGBT gate terminal with that low of a resistor.

[MPaulHolmes]

motor amps * pwm duty = battery amps. So, if you tried, say, 20% of full throttle, the pwm duty would ramp up until the current feedback was 20% of the max current. I'm not sure what the software was, but on a 0.75" x 0.375" bus bar, the full range of that current sensor (assuming the melexis HB) is 0 to 1200 amps or so. That would mean you commanded 20% of 1200 amps from the Battery pack. The motor amps can be very very large when the battery amps are small. So, while the pwm was ramping up, in the vain attempt to see 20% of 1200 amps (or whatever), the motor amps would have been very large near zero rpm.

[cpate]

@bjfreeman: if you mean freewheel diodes across the motor, I am indeed using the upper half of the IGBT module for this purpose.

@subcooledheatpump: I'm not sure what exactly you mean by "crazy gate connections." I will try switching out the resistors for ones with higher values.

I am using the firmware modified for a hall throttle and 8khz PWM.

Thanks for answering, paul! The thing about the motor current is, we were testing the controller with a stove burner, which is basically the same as a resistor as far as I know. The 30 ohm resistance of the burner we were using limits the current that can pass through it at 144v to about 5 amps. Is it possible that the heating coil has enough inductance to blow the IGBTs?

[badfishracing]

The side of the IGBT that you're using as the freewheeling diode, the side that you didn't connect to the driver, should have the gate and emitter tied with a jumper instead of a 10K resistor? Might not be an issue though. The 10K might be enough to keep it off.


Darin

[MPaulHolmes]

Oh, the burner was from B+ to M-?

[badfishracing]

Originally Posted by badfishracing

The side of the IGBT that you're using as the freewheeling diode, the side that you didn't connect to the driver, should have the gate and emitter tied with a jumper instead of a 10K resistor? Might not be an issue though. The 10K might be enough to keep it off.


Darin

Probably not a big factor, but I believe the normal inductance in the motor is an important part of the igbt/cap/diode power trinity. So straight resistance isn't really the load you want to use.


Darin