Selective Harmonic Minimization in Asymmetric Cascaded Multilevel Inverters using Soft Computing Methods

Abstract: Multilevel Inverters (MI) achieve the desired output voltage by suitable combination of low dc variable voltages at the input side. The fundamental output voltage can be controlled and the undesirable lower order harmonics of stepped voltage waveform can be eliminated by applying Selective harmonic Elimination (SHE) Method. In this method, the commutation is provided for semiconductor switches on fundamental output voltage at predetermined angles. This paper proposes a Fuzzy Logic Controller to regulate the output voltage waveform of multilevel inverter with reduced harmonics. At first the Particle Swarm Optimization (PSO) algorithm is used to evaluate switching angles for different combination of input voltages applied to MLI and then a fuzzy controller is designed using PSO results to achieve the desired Fundamental output voltage and eliminate the low order harmonic for entire range of dc input voltage sources variation. The proposed FLC controlled method is carried out for a wider range of input dc voltages by considering ±10% variations in nominal voltage values to design 7 & 9-level inverter to validate the results obtained.

Keywords: H-bridge Multilevel Inverter, PSO, Fuzzy Controller, SHE method, THD.