Highly stable power supply using digitally controlled phase-controlled rectifier and active filter

Abstract

A design of a highly stable current-controlled power supply combining a phase controlled rectifier (PCR), passive filter and active filter is investigated. A digital phase-locked voltage control (PLVC) with a capability of compensating the thyristor firing angles under an unbalanced power source is proposed; otherwise the PCR output voltage has low-order subharmonics whose suppression requires a bulky passive filter. The digital PLVC has a fast dynamic characteristic as an inner control loop of the PCR. To suppress further the output ripple, an active filter using a transformer is introduced and its design is described through a frequency-domain analysis. An optimal, proportional and measurable-variable feedback (IPM) controller is designed using a time-weighted performance index based on a time-domain analysis. The design method based on the time-weighted performance index gives a better response characteristic than that based on the conventional performance index. It is shown via experimental results that the proposed scheme gives good dynamic and static performance.