Investigation of the Current Turn-off Characteristics of a GTO Thyristor in an Inductive Pulse Forming Network

Abstract

Abstract : The project investigated of the current interruption capability of Gate Turn Off (GTO) thyristors, specifically, factors that had potential to increase the amount of current that could safely be turned off. A series of GTO thyristors were used in an inductive pulse forming circuit to interrupt varying amounts of current. The test circuit consisted of a high-voltage capacitor bank, a wire-wound inductor, the GTO thyristor with control circuitry, and instrumentation to measure voltages and currents in the circuit. The capacitor bank supplied energy for each current pulse while the inductor controlled shape and duration of the current pulses; control circuitry determined timing of current pulses used to turn the GTO thyristor on and off. The test circuit utilized a conventional H-bridge driver to control turn on and turn off of the GTO thyristor with each leg of the H-bridge connected to a dedicated capacitor bank to supplied energy for current pulses. The H-bridge allowed shape and magnitude of the turn-off gate current pulse to be easily adjusted. The amount of gate turn-off current was adjusted to determine if the current interruption capacity of the GTO thyristors could be increased beyond their turn-off current rating. The project demonstrated that the GTO thyristors were capable of reliably interrupting twice their nominal turn-off current rating. Furthermore, the turn-off speed of the GTO thyristors is dependent upon the amount of gate current used to turn off the GTO thyristors. The GTO thyristors that were turned off using larger gate currents were able to interrupt higher levels of current and turn off faster than the GTO thyristors that were turned off using smaller gate currents. This project complements work on railgun pulse power systems. Inductive power supplies may provide a solution to the energy density requirements of electric weapon systems. This investigation demonstrates GTO thyristors can be used in inductive pulse power supplies.