Optimized harmonic elimination for cascaded multilevel inverter

Abstract

Optimized Harmonics Stepped Waveform Pulse-Width Modulation(OHSW-PWM) for high voltage high power cascaded multilevel inverter with equal DC sources are commonly used in constant frequency utility applications. Stepped switching angles for cascaded multilevel inverter are calculated by solving nonlinear equations to eliminate preselected lower order harmonics. This paper proposes a generalized method to calculate the switching angles based on Newton-Raphson method for solving the nonlinear equations, which are transcendental in nature and multiple solutions exist. Calculations of the switching angels are performed by anticipated formula for calculating the initial angles values. This paper presents solutions for 5, 7, 9, 11, and 13 multilevel inverters under different values of the modulation index using Matlab software. The results reveal that Newton-Raphson method can be effectively used to calculate the switching angles that eliminate the selective lower order harmonics from the MLI output voltage and reduce the total harmonic distortion. The experimental and simulated results proved the effectiveness of the proposed method. © 2013 IEEE.