Driving high inductance Solenoid using H-Bridge

[koniho]

I've been building an IGBT based H-Bridge using irs2108 drivers. I've varied the model of IGBT around in hopes of over coming a problem that I've been having of IGBTs exploding. With much frustration I think I've narrowed the issue down to the Voltage build-up when switching the bridge into the free-wheeling "off-state". I'm planning on running the system at 300V but so far, I've been running into issues around 180V. Power supplies all look clean and the driving logic has been verified. The HS and ~LS signals of the irs2108 are driven by the same signal so that the shoot-through condition should not occur unless driver is damaged.

What I'm seeing is that the IGBT's go into a latch up mode or similar and hit a short circuit fault until they burn up in a puff of magic smoke.

My next inclination was to place a snubber network in parallel with the load but as far as I can see on the scope, there's little improvement in the turn-off voltage transients. I've read many application notes now on snubber networks across the IGBTs but they seem to be mainly concerned with reducing the switching losses. In my application, I'm only switching the solenoid 'on' with a short 5-50ms pulse and not doing any PWM.

The last thing I've tried was a Varistor in parallel with the load and I did see improvements in suppressing voltage transients but once I upped the voltage to 180V, I again experienced an explosive bridge.

If anyone has experience with driving a highly inductive load with an h-bridge using IGBT's I'd love to hear your input on my problem. Thanks!

Attached is the H-Bridge schematic:

https://lh3.googleusercontent.com/_...kN024/s800/10seg_2dir_actuator_oneChannel.png

 

[(*steve*)]

Just wondering if your IGBTs include an integral free-wheeling diode or if you've got them externally?

Latchup can be caused by excessive drain current, something that is likely with a capacitive load, but not with an inductive load.

Another possibility is shoot-through which has a very high risk of also leading to latchup, regardless of the load. Do you have dead time between switching of the IGBT's?

 

[koniho]

Just wondering if your IGBTs include an integral free-wheeling diode or if you've got them externally?

Latchup can be caused by excessive drain current, something that is likely with a capacitive load, but not with an inductive load.

Another possibility is shoot-through which has a very high risk of also leading to latchup, regardless of the load. Do you have dead time between switching of the IGBT's?

The IGBT's do have integrated free-wheeling diodes. I've also tried IGBT's without and used external diodes in the case that the integral diodes were failing.

The irs2108 has internal shoot through protection via dead time. I think the next step is to investigate snubbers on each igbt.

 

[(*steve*)]

I might try removing 2 of the IGBTs, so the half bridge can only supply power in one direction, and see if they latch up. If they do, then this would likely be why they fail. However it's possible that latchup won't occur in this arrangement -- if it does though, it will be less dramatic.

Is the failure associated with a high current draw? is the supply protected by anything (a fuse perhaps)?

I'd be trying to determine if it is a latchup problem first.

Is the failure really explosive? Or is it copious smoke? Do they fail in pairs? or all four at once?

 

[koniho]

I might try removing 2 of the IGBTs, so the half bridge can only supply power in one direction, and see if they latch up. If they do, then this would likely be why they fail. However it's possible that latchup won't occur in this arrangement -- if it does though, it will be less dramatic.

Is the failure associated with a high current draw? is the supply protected by anything (a fuse perhaps)?

I'd be trying to determine if it is a latchup problem first.

Is the failure really explosive? Or is it copious smoke? Do they fail in pairs? or all four at once?

The failures are mostly really explosive, indicative of an overvoltage and not an overcurrent condition (as far as a I can tell) Most of the failures have affected all four IGBTs at once. It's worth noting that the IGBT's are TO-220 without heatsink. For my application, the short pulse of current is not enough to significantly derate the IGBTs.

I'll do some experimentation to determine if latchup is a problem.