Study of low ripple Dc power supply for superconducting coils

To excite a dc superconducting coil for a fusion plant, a high output current and low voltage power supply is necessary. For this purpose, a thyristor rectifier is widely used but its output voltage includes a large voltage ripple and sometimes the voltage ripple affects the sensitive detector such as a quench detector. Especially, in a steady state operation, the coil terminal voltage becomes zero in which condition the voltage ripple becomes maximum. In this paper, a ripple compensator, that is PWM converter connected in parallel to the rectifier, is studied for this ripple reduction. The required current for the converter is estimated and is shown that it become 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.