Multi-physics Analysis Of ITER External Bypass Cabinet By Heat, Electricity, Magnetic

ITER external bypass cabinet is an important component of the rectification power supply system, it is an important equipment that protect magnet and power from over-current and over-voltage. External bypass cabinet adopt pulse operation mode, and a big DC current will flow in a very short time. In the worst case, the maximum peak pulse current may reach about 300kA. Therefore, ensuring current sharing between the bridge arm in such a high current flow and dynamic stability of the bypass cabinet are challenging technical problems. And the cabinet cannot be directly purchased on the market at present, so we must mainly rely on our owm effort to design and develop the cabinet.Firstly, the type of thyristor in the bypass cabinet is selected, then the thermal model of thyristor is established in the paper. The design purpose that prevent the thyristor junction temperature overheating is proposed. The number of parallel thyristors is finally determined through the establishment of thyristor thermal impedance and transient thermal impedance combined with thyristor dissipation power and junction temperature calculation method. Then, the temperature rising process during a single thyristor is analyzed according to the work status of the external bypass cabinet.The circuit model of the external bypass cabinet is established, and the parasitic parameters are detailedly calculated. The influence on the dynamic DC current sharing of the external bypass cabinet that parasitic parameters of the circuit, thyristor on-state voltage drop and thyristor temperature produce is analyzed,then, several measures of current sharing are proposed. All of them are used to provide theoretical support for the external bypass cabinet structure design and the device selection.The electromagnetic model of the external bypass cabinet is established, and simplified 3D CATIA model is given according to the design, then the CATIA model is imported into the COMSOL. Finally, electromagnetic and dynamic stability and current sharing are analyzed by COMSOL, and the rationality of the design is confirmed.