Research Of The Switch Network Unit System Base On Hybrid DC Switch Of CFETR

The China Fusion Engineering Test Reactor(CFETR)is the next generation superconducting fusion experiment project of China,and the Switch Network Unit(SNU)is its key subsystem for establishing plasma.Based on the hybrid DC switch technology,the thesis comes up with a novel SNU topology to meet the parameter requirements up to 80 k A/20 k V.Besides,the key issues such as device selection,parameter design and reliability are also studied in the thesis.This thesis compares the characteristics of each DC switch technology and designs a new SNU topology based on the hybrid DC switch for the CFETR.The SNU includes three parts: by-pass switch,solid-state switch and discharge resistance.The solid-state switch is composed of controlled semiconductor switches and thyristors,and an auxiliary capacitor is used to ensure the reliable turn-off of thyristors.In this topology,the number of controlled semiconductor switches in series is small,the system reliability is high,and the turn-off process is simple.Then,this paper deeply analyzes the characteristics of each semiconductor device and selects IGBT and fast thyristor as the semiconductor switch in SNU.Combined with the working characteristics of the SNU,the key parameters such as the capacitance value of the auxiliary capacitor and the number of semiconductor switches in series and parallel are determined.Based on the behavior model of the semiconductor device,the SNU simulation model is built.The simulation results show that the topology can complete the commutation process and establish the voltage within 15 ms,which meets the CFETR SNU design requirements.When the stray inductance of the solid-state swith branch and the auxiliary capacitor branch is 10 μH,the IGBTs in the solid-state switch only need to withstand 41% of the total SNU voltage.Besides,reducing the stray inductance can further reduce the voltage that the IGBTs needs to withstand,which is beneficial to reduce the number of IGBTs in series.Finally,the reliability analysis of each semiconductor switch component in SNU is carried out.In order to improve its reliability,a redundant design was carried out based on the k/n(G)model.With the redundancy,the reliability indexes have been improved significantly,especially the high reliability life has been increased several times or even dozens of times.The research results of this thesis provide a feasible scheme for CFETR SNU and can also provide an important reference for the design of other high-power DC switches.