A Novel Ultrafast Turn-Off Failure Detection Method of Integrated Gate Commutated Thyristor for VSC Application

Integrated gate commutated thyristor (IGCT) has prospects in voltage source converter application. However, it has no desaturation characteristic in conducting state like insulated gate bipolar transistor, for which fast turn-off failure detection for blocking converter in deadtime is of great significance. In this letter, an ultrafast IGCT turn-off failure detection method is proposed. First, turn-off process and failure mechanism of IGCT is analyzed. It is clarified that turn-off capacitors of gate driver will continue to discharge in turn-off failure, thus generating a voltage drop on turn-off mosfet, which can be the criterion of failure. Then prototype, threshold and timing sequence are designed. Analog circuit including amplifier, hysteretic comparator and reference circuit is used for fast and accurate measurement of voltage on mosfet. The failure gate current and fall time of turn-off trail current is measured in pulse test. Finally, experiments are carried out to verify the feasibility of the proposed scheme. The results show that the proposed scheme can achieve reliable turn-off failure detection within 19 microseconds. Neither false detection nor missed detection occurred. Proposed method has great accuracy and rapidity, and is convenient in implementation. It will greatly decrease the extreme failure rate of IGCT-based converters.