Application of optimization technique in SHE controlled multilevel inverter

Application of Particle Swarm Optimization algorithm for finding the optimal solution of switching angles in a 3-ph seven level Cascaded Multilevel Inverter (CMLI) with unequal DC sources for elimination of lower order harmonics is presented in this paper. For Cascaded Multilevel Inverter, the common switching technologies such as low frequency Selective Harmonic Elimination-Pulse Width Modulation (SHE-PWM) technique and Optimal Minimization of Total Harmonic Distortion (OMTHD) techniques are applied to obtain staircase voltage waveform. SHE-PWM based approach is used to maintain desired fundamental component of output voltage and to reduce specific lower order odd harmonics. Whereas OMTHD is used to minimize the overall THD. The lower order odd harmonics cannot be eliminated easily as it contains non linear transcendental equations derived from Fourier series expansion. Solutions to these equations are complex and time consuming. In this paper, to solve these nonlinear equations PSO algorithm has been implemented. Simulation of seven level CMLI with unequal DC sources with proposed algorithm in MATLAB/Simulink environment is performed to validate the results.