Mayuko Koga

We propose an electric circuit that generates a high magnetic field with a variable pulse width using insulated gate bipolar transistor (IGBT) switching. One method to realize a magnetic field with a variable pulse width is to switch the circuit open and short using semiconductor devices. However, in the case of a coil load used to generate a high magnetic field, inductive energy is released as a surge voltage during high-current switching, which can lead to the failure of switching devices. Therefore, we proposed connecting an external circuit in parallel with the coil to absorb and dissipate the inductive energy and analyzed the surge voltage and current waveforms generated in the circuit. The analytical solution based on circuit analysis and the circuit simulation results showed good agreement, indicating the transient response waveforms of the current and surge voltage in the proposed circuit. Moreover, the results reveal a trade-off between the surge voltage and the current decay time constant, depending on the resistance and capacitance values of the external circuit. A switching circuit with anti-series connected IGBTs demonstrated the interruption of the discharge current (500 A peak, 1 ms FWHM pulse width, 3 kV surge voltage) at arbitrary timing for driving the magnetic field. From these results, a pulsed magnetic field with a variable pulse width was implemented.