Impact of Practical Issues on the Harmonic Performance of Phase-Shifted Modulation Strategies for a Cascaded H-Bridge StatCom

Phase-shifted carrier (PSC) modulation has become an industry standard in its application to multilevel H-bridge static compensators (H-StatComs). The technique uses the cancellation of harmonics within each phase leg to significantly improve the harmonic performance relative to the switching frequency. This paper investigates subtle practical implementation issues which deteriorate the harmonic performance of this technique. The effects of nonuniform dc bus voltages and capacitor voltage balancing strategies are investigated. Simulation and experimental results are presented which show that the harmonic performance of the PSC technique deteriorates as the number of voltage levels produced by the H-StatCom increases.