A novel method for reducing harmonics in series-connected rectifiers

A novel method for reducing harmonics in series-connected converters is proposed in this paper. Pulse multiplication for parallel-connected converters is usually easier to achieve because of the interphase transformer, which is absent in the series-connected converters. The proposed method in this paper adopts an averaging inductor to the series-connected converters and thus simplifies the pulse multiplication circuit greatly. The principle of this method is demonstrated by a three-thyristor switching circuit scheme, which can make a 12-pulse double bridge converter to operate at 36 pulses. Simulation results reinforce the theoretical work. Only slight changes are needed for the proposed method to reach higher pulse operations. This makes this method even more attractive when high-pulse operation is desired. The configurations of two-thyristor and four-thyristor switching schemes are also given.