Protection scheme for igbt short circuit

[sheraz83s]

Hi
I am using IR2113 gate driver ic for my inverter application.My igbts are from semikron.I need a short circuit protection in my design as there is no embedded feature for protection in ir2113.I am working with LEM55 for my current sensor and designed a comparator circuit to shutdown ir2113.But its hard switching.Can one suggest better idea ?

 

[schmitt trigger]

Don't understand exactly what you mean by hard switching, can you elaborate?

Anyways the IR2113 has a shutdown circuit that its latched. Which means that once it is disabled (via your comparator) it will remain like that until the next trigger pulse arrives which resets the latch.
So essentially you'll have repetitive very high current pulses for as long as the short circuit condition remains in place, this could lead to hot spots on the IGBT...is this your concern?

 

[sheraz83s]

Don't understand exactly what you mean by hard switching, can you elaborate?

Anyways the IR2113 has a shutdown circuit that its latched. Which means that once it is disabled (via your comparator) it will remain like that until the next trigger pulse arrives which resets the latch.
So essentially you'll have repetitive very high current pulses for as long as the short circuit condition remains in place, this could lead to hot spots on the IGBT...is this your concern?

There are two type of switching on/off characteristics soft switching and hard switching...in soft you turn on the device with zero voltage switching and zero current for turn off.by shutting down the gate driver during fault condition cause hard switching and due to large current the device can damage also.so i need to design a protection circuit which works well for fault case and also eliminate stress on device.

 

[schmitt trigger]

Indeed, I understand the difference between hard and soft switching.

The way the original sentence described the problem confused me. But I now understand what your problem is.

You may require a "pilot" IGBT in parallel to the main IGBT to briefly carry the fault current while the main IGBT turns off. I had seen once such a scheme, but don't recall the actual circuit details other than the pilot IGBT had some sort of current limiting network. Otherwise the pilot IGBT itself would be destroyed.

 

[FvM]

IGBTs will be preferably controlled with bipolar gate voltage. If you also want short circuit protection and desaturation detection, a full featured gate driver IC instead of simple IR21xx would be suggested.

 

[mtwieg]

Your options depend on what sort of response time you need. A fast LEM with external logic may be fast enough to save the IGBT from a bad short circuit, but only if it latches the fault so you don't get repetitive shorts. Desaturation detectors built into the gate driver can also be helpful.

 

[sheraz83s]

Thanks all for your replies.
Yes, you are right to select ic with builtin sat detection pin.It is difficult to find another gate driver ic and make new pcbs.As my design. IR2113 provide +15V and 0v for turn on and turn off.Bipolar voltage surely solve the problem and minimize the time.I am using a higher IGBT like 1200V and 150A current rating which is quite above the design of single phase 400V bus voltage and 5Kw single phase inverter application.If i have some more time i will definitely go for infineon gate driver Ics or IRF for better performance and features.
According to my understanding if i use higher rated device and fault occurs,then hard switching will not be a big problem and device will not be in much stress in those conditions.Am i right here ?

 

[FvM]

According to my understanding if i use higher rated device and fault occurs,then hard switching will not be a big problem and device will not be in much stress in those conditions.Am i right here ?

Hard switch-off of shorts can be a problem due to generated overvoltages. It's usually not a problem in bridge topologies with low inductance DC bus and some voltage margin, because the overvoltage is diode-clamped. In addition, the short circuit handling of intelligent gate drivers often uses soft switch-off to reduce dI/dt índuced overvoltages.

According to the IGBT characteristic, the built-in desaturation detection acts on a relative large overcurrent level. An output current sensor gives the chance to cut shorts nearer to the regular operation current without causing stress to the IGBT. This is particularly the case, if the output dI/dt is limited by an inductor in the application circuit. This kind of overcurrent protection is usually located in the control signal generation, e.g. current control loop or PWM circuit rather than the gate driver. Error latching should be also provided on the controller or pwm generator level.