Parameter Optimization of Thyristor Snubber Circuit in LSTF Quench Protection System

The Large-scale Superconductor Test Facility (LSTF) is an important part of comprehensive research facilities in support of China Fusion Engineering Test Reactor (CFETR). In order to protect the superconducting magnets from being damaged in quench accident, the Quench Protection System (QPS) should be designed to commutate the energy stored in the coils. The snubber circuit is used to reduce the reverse recovery current and voltage of thyristor in QPS, and it can impact the reliability and stability of the QPS. In general, the studies of snubber circuit are focused on the DC turn-off process of thyristor used in HVDC, which has small turn-off current. However, the turn-off current can reach to 100 kA in the QPS of LSTF. In this paper, a thyristor reverse recovery model is described, and the key parameters of reverse recovery current are obtained from the testing experiment. Based on the transient analysis of snubber circuit, a systematic approach is used to minimizing the resistance and capacitance of snubber circuit of QPS working condition is proposed. By the MATLAB simulation and comparison, minimum parameters of snubber circuit were obtained, and proved that the approach can improve the reliability and stability of system, while reduce the cost of QPS.