Diode-Assisted Gate-Commutated Thyristor for Hybrid MVDC Circuit Breaker Applications

This work presents an analysis of the turn-off capability of a diode-assisted gate-commutated thyristor (GCT) for the application in a hybrid circuit breaker for medium voltage (MV) direct current grids and a design guideline for constructing a prototype, which fulfills all turn-on and turn-off conditions for this application. Mechanical and electrical simulations are conducted to optimize its behavior in a circuit breaker. Based on this, a prototype with a commutation loop stray inductance of 942 pH, which is a reduction of 84.7% and specially radiated diodes with a 260% higher forward voltage drop is constructed. The unity gain turn-off capability is modeled. The simulation is verified with experimental results and predicts a turn-off capability of 10 kA. The evaluation of the turn-off experiments revealed a second turn-off criterion, which requires a symmetric snubber setup. This is not a necessary condition in IGCTs. Addressing this criterion the prototype successfully interrupted 1.2 kA. The device failed at 1.3 kA because the used wafer is not rated for higher currents. The necessary turn-off conditions regarding the design of the commutation path and the device package however, are fulfilled. Therefore, higher turn-off currents with a higher-rated wafer are expected.