An adaptive SPWM technique for cascaded multilevel converters

An adaptive carrier based sinusoidal pulse width modulation (SPWM) technique for cascaded h-bridge (CHB) multilevel converters is presented in this paper. The proposed technique enables the CHB topology to provide a symmetrical ac voltage from a set of time-variant input dc source voltages. Two alternative approaches, namely the single-carrier and dual-carrier algorithms, are described for implementing the adaptive SPWM technique. The two algorithms differ in the number of voltage sensors required, leading to differences in transient behavior and implementation, though they produce identical steady-state results. The voltage level diagram as a tool to facilitate the customization of adaptive SPWM steady-state behavior is also introduced. The techniques presented in this paper generalize to any number of cells and are inherently tolerant to faults in power sources and cells, i.e. a source or cell fault causes the necessary switching states to be bypassed. Software simulations are presented to demonstrate the efficacy of the presented algorithms.