| The research and development of commutation circuit of quench protection system in large superconducting device is one of the core research work of the Comprehensive Research Facility for Fusion Technology(CRAFT)project.According to the requirement of 100 kA/10 kV bi-directional DC breaking and 10 GJ energy dissipation proposed by superconducting magnet test platform for quench protection system,the project of super large capacity DC breaking and commutation scheme are design,and also the commutation circuit equipment of the system is design.In this paper,a new H-bridge structure converter circuit topology is proposed based on the study of the design schemes of quench protection system for large superconducting devices at home and abroad,and DC circuit breaker in DC power grid.Also,the selection and layout of control components are designed.Based on the study of the commutation process,the detailed transient analysis is carried out,which provides theoretical research support for the parameters design and optimization of the commutation circuit.Based on the transient analysis of the system commutation process and the research on the process of the vacuum arc burning and the dielectric recovery process,this paper analyzes the influence of the parameters of the commutation circuit on the dielectric recovery process after the breaking of the vacuum switch in the main circuit of the system.According to the continuous transition model of sheath development,the limit parameters of commutation circuit are determined.A multi-objective parameter optimization method for the commutation circuit of the artificial zero-crossing type quench protection system is proposed by considering not only the restoration ability of the medium behind the vacuum arc,but also the breaking speed and equipment cost as the secondary objective.According to the 130-kA high frequency pulse condition of the commutation circuit,this paper designs the trigger unit-thyristor switch of the commutation circuit.The temperature rise of different types of thyristor devices are simulated based on the Cauer thermal circuit model firstly.According to the results,the device is preliminarily selected and the series structure is designed.Aiming at the switching off overvoltage of thyristor,the parameter optimization method of snubber circuit under pulse condition is proposed,which not only improves the suppression ability of recovery voltage,but also takes into account the cost performance.Through the experimental comparison of different types of thyristor breaking performance,the short board and reasons of pulse power devices in the system commutation circuit application are obtained,and the structure design scheme of thyristor switch is finally determined.In addition,considering the requirements of application conditions,a new 130-kA dry type air core pulse inductor is developed.Considering the extremely strong magnetic field generated in the discharge process,the magnetic field around the inductor,the electromagnetic load of the coil and the electromagnetic structure coupling are simulated.also,the coil terminals are optimized based on the simulation conclusion.Also,as the requirement of high life,a set of the fatigue analysis of the reactor are carried out,and the expected life and the most vulnerable point of the inductor are calculated and simulated.Finally,the development and test process of the inductor are introduced briefly.At the end of the paper,the combination experiment of the developed commutation circuit and the applied vacuum switch is carried,which proves the validity and reliability of the proposed new topology,parameter optimization method and electrical equipment design.The proposed research work fills the gap in the field of ultra large capacity development of quench protection system,ensures the safe operation of superconducting magnet in extreme test environment,and provides strong support for the development of fusion reactor in the future. |
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