Harmonic Reduction in Cascaded Multilevel Inverter

Abstract

— This paper presents method of selecting switching angles of a cascaded multilevel inverter so as to produce required fundamental voltage along with improved staircase waveform in terms of harmonics. Cascaded multilevel inverter uses number of DC sources, for k sources number of levels will be 2k+1 and leads to k number of non-linear equations to be solved. Many approaches can be made regarding the solution but this paper focuses on Specific Harmonic Elimination (SHE) technique for angle optimization. Newton-Raphson method is used and the difficulty with this method is a closed initial guess. Variation of angles with modulation index is observed and THD is calculated for selected modulation indexes and all attempts are made so as to get lowest THD. Results are simulated in MATLAB/Simulink environment. Index Terms -Cascaded multilevel inverter, SHE, Switching angles, THD.