| High power converter is one of the key equipment of the Comprehensive Research Facility for Fusion Technology(CRAFT)project proposed in the 13th five-year plan of China.Based on the requirements of stable output and 4 times rated current overload operation of superconducting magnet power supply,the research and design of CRAFT converter system are developed in this paper.The main contents and innovations of this paper are as follows:Based on the operation characteristics of superconducting magnet,the operating range of CRAFT converter is analyzed,which provides guidance for converter operation.In order to ensure the reliable protection of superconducting magnet,the design method of system parameters and core devices of superconducting fusion converter is studied by detailed theoretical and simulation analysis and calculation,and the technical difficulties of high-power fusion power supply system meeting high-energy output,extreme protection and stable and reliable operation are solved.Based on the demanding fault suppression capability of superconducting fusion converter,the structural dynamic thermal stability of CRAFT converter under large fault current is analyzed by electromagnetic structure temperature coupling analysis under high current and temperature.In view of the complex structure and difficult design of multi high power device paralleled device,different design schemes are compared and analyzed,and the temperature distribution law of high current converter is studied,which provides the idea of fluid structure coupling analysis of the whole structure.Aiming at the problem of local overheating at the contact position of high current DC busbar,a fast estimation method of contact temperature based on heat transfer theory and Thermal-Electric module is proposed and verified by experiments.Compared with the electric contact Voltage-Temperature method,this method proposed in this paper has the advantages of high efficiency and global in temperature estimation of high-power water cooling equipment.Based on this method,the relationship between flow velocity and contact resistance of CRAFT DC busbar is studied,which solves the technical challenge of difficult to estimate contact temperature of water cooling equipment and avoids unnecessary cooling loss.Based on the transient overload operation requirements of superconducting magnet converter,a calculation method of the maximum pulse current of multi parallel converter system is proposed.The correctness of the method is verified by comparing the results of calculation,simulation and experiment by combining the two conditions of device bearing capacity and system output capacity.Based on this method,the maximum pulse current and operating range of CRAFT converter system under different parallel number and time length are studied,which makes it have dual functions of steady-state output and transient overload operation,and greatly improves its utilization efficiency.The possible neutron irradiation of converter in deuterium tritium fusion is studied.Based on the high flux neutron irradiation experiment of thyristor,the reason of the difference in electrical characteristics of thyristor before and after irradiation is analyzed.The abnormal operation of superconducting fusion converter in neutron irradiation environment is pointed out,and the corresponding protection scheme is proposed. |
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