Comprehensive Harmonic Optimization in Cascaded H-bridge Multilevel Inverters Using Variable DC Sources

OMTHD and SHEPWM strategies are two prevalent methods, have been independently exploited for voltage harmonic reduction in multilevel inverters. While both aforesaid methods are effective, obtrusive presence of low order harmonics after THD minimization and considerable overall harmonic level after elimination of selected harmonics, can be sometimes troublesome. Moreover, inexistence of feasible solution for the entire range of modulation indices is also another possible problem. This paper presents a comprehensive formulation for harmonic rejection and output voltage improvement in multilevel inverters. Simultaneous, depending on the emphasis weighted, THD minimization and low order harmonics rejection, considering regulation of the fundamental voltage, are advantages of the proposed method. Furthermore, alterable DC sources are considered for harmonic optimization in the output waveform. A relatively new, Bat-inspired metaheuristic algorithm is utilized to solve nonlinear equations. The comparison of simulation results with standard OMTHD and SHE switching strategies, validates the efficaciousness of the proposed scheme.