This paper describes an application of a protection circuit by using gate charge characteristic against hard-switching fault (HSF) to three parallel connected IGBT modules. The gate charge characteristic under HSF differs from that under normal turn-on operations because the gate-emitter voltage has no Miller plateau under HSF. Hence, HSF can be detected by monitoring a gate-emitter voltage and a gate charge. IGBT modules can be protected from destruction by using one detection circuit arranged in the middle of the IGBT modules connected in parallel because the gate charge characteristic of each IGBT modules connected in parallel is almost the same. The validity of the protection circuit by using gate charge characteristic is verified by experimental results. Experimental results have confirmed that the proposed circuit can turn off the IGBTs within about 800 ns later after the collector current starts flowing through the IGBT. This paper reveals that the method is applicable to three parallel connected IGBT modules.
