So I plan on putting this inverter module in my college's Power Electronics lab. Hence the emphasis on protection.
To ensure that no matter what signal is applied by the user, the inverter should not get damaged, I have decided that only the 3 High side gate inputs shall be available to the user. Getting the complementary signals for the Lower switches and insertion of suitable dead time shall be done inside the module and will be hard wired in.
I was thinking of a circuit along the following lines.
This will be an independent block with following inputs - H1, H2, H3, OC/SC signal, Thermistor signal, Precharge signal.
Outputs will be all the 6 gate signals which according to my calculations should all go low in less than 70-80ns, based on individual propagation delays of 74 series logic ICs, in case any of the 3 fault/precharge signal goes low.
The driver is not finalized yet but if I go for a driver with built in desaturation detection, it will act as a second line of defense in case of a short circuit.
Please take a look and provide valuable suggestions.
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Should I just skip the OC/SC sensing externally and solely use the ACPL driver IC's DESAT fault detection system? I will still use above circuit for precharge and thermistor.
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Ok I just read that the DESAT system resets after 25us. So in case of a sustained fault/SC, it will oscillate I imagine which definitely cannot be good. What to do?
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OK now this has got me thinking. I now realize that all the protection schemes I've come across reset very very fast, be it fixed time as is in this case, or be it using the hysteresis based protection schemes where the gate drive is re-enabled once the SC current falls below a certain level.
But then what happens in case there is a dead short? This constant turning on and off of the IGBT doesn't damage it?
Also soft shutdown during fault to prevent excessive inductive over voltages across the IGBT. Please throw some light on that in regard to how it is generally achieved, for say a cheap driver like TLP250 where that logic will have to be applied using external circuitry.