Optimal Pulsewidth Modulation of Nine-Switch Converter

Nine-switch converter is a recent reduced semiconductor topology proposed in place of the back-to-back 12-switch converter. Like its precedence, the nine-switch converter can either operate at a single common frequency (CF) or different frequencies (DFs) at its two sets of three-phase terminals, but because of its reduced-switch configuration, some compromises cannot be avoided. In particular, the nine-switch converter is more restricted in its total attainable amplitude and phase shift between its two terminal sets, which means that when migrating standard modulating theories to the nine-switch converter, more concerns have to be addressed. These concerns are now investigated in the paper, before knowledge on how to avoid unintentional distortion and appropriate modulation schemes are formulated for operating the nine-switch converter in its CF and DF modes. Explanation, simulation, and experimental results are all presented in the paper for verifying the conceptual standing and practicality of the proposed modulation schemes.