Optimal firing-angle control of cascaded HVDC converters for minimum harmonic currents

Abstract

An optimal firing strategy for N cascaded, 6-pulse, phase-controlled power converters of a HVDC link is proposed. Minimization of the harmonic currents injected into the AC system (by both the inverters and rectifiers) is achieved through simultaneous control of the firing angles of the N power converters. With relatively low values of N (4 12-pulse, or 8 6-pulse), the resultant AC current harmonics are substantially lower than for comparable 12- or 6-pulse converters. Also, the DC voltage harmonics are greatly reduced over 12-pulse operation.<>