Nonlinear Characteristics of Metal-Insulated REBCO Magnet Under Various Switching Frequencies of Half-Bridge Inverter Circuit

This paper presents the experiment and analysis on the control of current in Metal Insulation (MI) magnet using a DC power supply and power semiconductor components. A 3 V DC voltage is applied to the 37 mH class MI magnet in a liquid nitrogen environment, 77 K. The operating current is controlled using a half-bridge circuit with SiC MOSFETs and a PI control scheme. The switching frequency varies from 100 Hz to 40 kHz, while the duty cycle remains fixed at 0.5. Experimental results are analyzed using a conventional lumped circuit model which contains the characteristic resistance of No-Insulation (NI) class magnets. Lumped circuit parameters that best describe the current measurement results are simulated using a genetic algorithm. According to the simulation results, as the switching frequency increases, there is a tendency for the inductance to decrease while the characteristic resistance increases. Based on the results of these parameters at different frequencies, a discussion regarding the limitations of the conventional lumped circuit in high-frequency switching scenarios is conducted.