Harmonic optimization in seven level inverter employing hybrid BBO/MADS algorithm

A hybrid optimization algorithm to find the optimum switching angles in a Multilevel Inverter (MLI) is proposed in this paper. The switching angles are optimized to eliminate low frequency harmonics. A seven level Cascaded Multilevel Inverter (CMLI) is considered and optimum switching angles are found by Hybrid Biogeographical based optimization search (BBO) / Mesh Adaptive Direct Search (MADS) algorithm. The low frequency Selective Harmonic Elimination-Pulse Width Modulation (SHE-PWM) technique and Optimal Minimization of Total Harmonic Distortion (OMTHD) technique are applied in order to reduce the switching losses. In SHE-PWM based approach, specific lower order harmonics are eliminated and fundamental component of output voltage is maintained at desired value. In OMTHD based approach the overall THD is minimized rather than eliminating specific low frequency harmonics. The various performance indices like phase THD, line THD, lower order harmonics eliminated in a CMLI are calculated from the optimized switching angles. A seven level CMLI is simulated in MATLAB/Simulink by using switching angles calculated from BBO/MADS algorithm. The FFT analysis of SHE-PWM and OMTHD approaches are compared and verified with the predicted values from BBO/MADS algorithm.