DC-side shunt active power filter for phase-controlled magnet-load power supplies

Phase-controlled thyristor rectifiers are still the preferred choice in high power applications. This paper shows that their steady state and dynamic performance can be greatly enhanced in high-precision and fast-response electromagnet power supplies by means of a shunt active power filter using a high-frequency PWM converter. In this hybrid structure, the rectifier is designed to handle the bulk of the output power, whereas the PWM converter is only used for harmonic cancellation and current error compensation under transient conditions. This results in a small power rating for the shunt active filter. A suitable control scheme is proposed and implemented in this paper for the rectifier and the PWM converter. Experimental results are provided to validate the proposed concept