Hybrid interleaved space vector PWM for ripple reduction in modular converters

This paper addresses the problem of optimizing space vector PWM (SVM) for interleaved, parallel-connected, three-phase voltage source converters to reduce total harmonic distortion (THD) of the total line current. A systematic approach is presented for designing hybrid SVM schemes involving multiple sequences, including those based on active state division, and different phase shifts to reduce current ripple. First, the effect of different phase shifts on the current ripple is investigated and it is shown that using standard phase shifts yields performance close to optimal. Second, a zone-division plot is generated based on all sequence-phase shift combinations. The plot shows spatial regions within a sector where a certain sequence-phase shift combination results in the lowest rms current ripple in one switching period, and thus represents the optimal hybrid scheme. Lastly, simplified, easy-to-implement quasi-optimal SVM schemes are derived from the zone-division plot based on specific application requirements, and their performances are compared with the optimal scheme. The application of the proposed approach to a two-converter case is discussed in detail. A simple, quasi-optimal SVM scheme is proposed for grid-connected applications with analytical and experimental results confirming significant reduction in current THD. Finally, extension to three-and four-converter cases is discussed.