Burning (turned to a wire) IGBTs in a three phase inverter b

igbt dc bus inverter

Hi Again.

I'm checking some measurments I took today, from the IGBT inverter bridge. The tests where made at a 50Vdc bus voltage. With the motor as inductive load. The dead time is 8us, automatically generated by the PWM module on the dsPIC.

The Image "print_11" are the gate signals of one IGBT branch.
Yellow: low side Green: High Side.
(You can see the cursors for the green channel from 50v to 65v.)

In a red circle you can see some noise (I think) Image "print_12", has a zoom of this "noise". There you can see, that it's under 50v, so no conduction of high side IGBT should take place.

Moving on to the Vce of the low side IGBT we have the waveform of the Image "print_14".
Yellow: Vce for low side IGBT Green: Gate signal.
Well theoretically when 15v applied to the gate I should see almost zero (a couple of volts) in the Vce. This is true for sections 1 and 2, but for sections 3 and 4, something else is happening.
Image "print_15" has a zoom in of the noisy area circled in "print_14"
As you can see there are some strange wave forms there.

I suppose this is cross conduction, but im not shure.
What can I do to solve this problem?

Thanks in advance.

Alex.

Re: Burning (turned to a wire) IGBTs in a three phase invert

Hi There,

From the looks of it, it looks like back emf generated from the motor. I am not really sure thou. I did sensorless PMBLDC motor driving and that slope looks just like the back emf that I am detecting to provide positional feedback.

Sorry but didn't really help you on your problem.

Rgds
sz

Re: Burning (turned to a wire) IGBTs in a three phase invert

I did not find any filter capacitor in 300V dc rail (100uF or more). IR2110 is not stable at high voltage hard switching. Try with TLP250.