Research on Reverse Recovery Transient of Parallel Thyristors for Fusion Power Supply

In nuclear fusion power supply systems, the thyristors often need to be connected in parallel for sustaining large current. However, research on the reverse recovery transient of parallel thyristors has not been reported yet. When several thyristors are connected in parallel, they cannot turn-ofi at the same moment, and thus the turn-ofi model based on a single thyristor is no longer suitable. In this paper, an analysis is presented for the reverse recovery transient of parallel thyristors. Parallel thyristors can be assumed as one virtual thyristor so that the reverse recovery current can be modeled by an exponential function. Through equivalent transforma- tion of the rectifler circuit, the commutating over-voltage can be calculated based on Kirchhofi's equation. The reverse recovery current and commutation over-voltage waveforms are measured on an experiment platform for a high power rectifler supply. From the measurement results, it is concluded that the modeling method is acceptable.