Design study of low ripple and large current dc power supply for fusion plant's superconducting magnet

The helical type fusion plasma test facility or fusion plant uses a large scale superconducting magnet system to make steady state magnetic field to confinement fusion plasma. To excite this magnet, a high output current and low voltage power supply is necessary. Also, this power supply is required a low ripple to avoid noise induced into the quench detector. As a large current power supply, a thyristor rectifier is widely used but its output voltage includes a large voltage ripple. Especially, it becomes maximum when the output voltage is zero and it is required in steady state operation of superconducting dc magnet. In this paper, a dc power supply which uses a PWM converter connected in parallel as a ripple compensator is designed for a fusion plant The required output current for the converter is calculated and is shown that it becomes relative smaller than the main rectifier, and the capacity of the converter is also relative small. A simulation is performed and it shows that this configuration suppress the current ripple of the rectifier.