GA optimization to mitigate voltage harmonics of cascade multilevel converters

The use of pulse width modulation with selective harmonic elimination (SHE-PWM) in cascaded H-bridges (CHB) multilevel converters allows the reduction of the output current distortion by the elimination of low order harmonic components. However, voltages produced by CHB modules to synthesize the SHE-PWM pattern is an issue that deserves deeper investigation. CHB systems fed by sources with current source characteristics, as photovoltaic strings operating with MPPT, may feature different source capacities. Thus, it is important that the energy provided by each module is proportional to the available energy, so input voltages remain balanced. This paper presents the development of a genetic algorithm (GA) to determine optimal waveforms to be synthesized by the CHB modules that ensures the equalization of the fundamental components, or even that a specific relationship between between them is achieved. Simulation results for five and nine-levels demonstrate the applicability of the technique, allowing the voltage balance of the DC buses to be addressed even in the modulation stage.