100 kA/10 kV thyristor stack design for quench protection system in CRAFT


 Thyristors have longer lifetime, higher reliability, less maintenance and very high voltage and current rating capabilities compared to other high-power semiconductor devices. As a result, it is very suitable for Quench Protection System (QPS), which protects the superconducting magnet in large fusion device from being damage. In this paper, the design of a 100 kA/10 kV thyristor stack is proposed by both theorical and simulation analysis and experiment verification. Due to the ultra-high electrical performance requirements put forward by Comprehensive Research Facility for Fusion Technology (CRAFT) to QPS, three main issues must be considered: the voltage-balancing problem brought from multiple thyristors in series structure, the junction temperature rising problem brought from extremely high current and reverse recovery phenomenon as the thyristor physical structure. Hence, a series of detailed theoretical analyses, simulations and experiments including thyristor junction temperature prediction method and reverse recovery process modeling are carried out to optimize the design scheme. Finally, the reliability and stability of the thyristor stack are verified by a series of prototype experiments. The results verify the correctness and accuracy of the proposed design methods of the thyristor stack, and also indicate that the proposed thyristor stack can meet the application conditions of 100 kA QPS in CRAFT project.