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 AC/DC converters. This paper shows that their steady-state and dynamic performance can be greatly enhanced for applications requiring high-precision fast-response performance by means of a hybrid structure using a shunt pulse-width modulation (PWM) active filter. 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 PWM converter. Experimental results are provided to validate the proposed concept.