Short Circuit Detection and Fault Current Limiting Method for IGBTs

Power devices may become damaged or even fail completely due to over-current caused by external factors such as ac line transients, mechanical overload, misfiring, inverter shoot-through, etc. Some of these incidents can result in a very high current (few times higher than the system's rated current) flow through the electrical drive system. Electrical machines have the capability to withstand very high current for relatively longer time duration (milliseconds to seconds depending on the size of the machine). On comparison, power devices, especially IGBTs, can withstand short-circuit current only for very short time durations in the order of microseconds and prolonged exposure can easily damage the power device. Industrial application requires proper short-circuit fault detection and protection circuits to protect the IGBTs from fault currents. Therefore, this article presents the fault detection circuit is based on monitoring the collector-emitter voltage using external collector capacitor, and the protection circuit is based on softly turning off the gate voltage using a current diode. The proposed method reduces power dissipation, temperature rise and prevents damage of the drive system.