Phase-Shifted Carrier Modulation Techniques for Cascaded H-Bridge Multilevel Converters

Phase-shifted carrier modulation is an industry standard in its application to multilevel H-bridge converters. The major advantage of this scheme over level-shifted and space vector modulation schemes is its inherent ability to evenly distribute losses between semiconductor devices. However, until now, its implementation has necessitated a capacitor voltage balancing scheme that degrades converter harmonic performance. This paper develops two phase-shifted carrier modulation schemes that avoid harmonic degradation by exploiting an extra degree of freedom in the available switching states. Simulation and experimental results are presented that confirm the correct operation of the modulation strategies.