Selected harmonics elimination in multilevel inverter using improved numerical technique

Abstract

For medium voltage high power application the modulation technique for power converters based on pre-computed Pulse Width Modulation (PWM) switching patterns can be very useful since the generated harmonic content can be previously known and optimize. The main challenge in applying harmonics elimination techniques at lower switching frequency is in solving the system of non-linear transcendental equations obtained by Fourier analysis. The numerical techniques offer simple solving procedure for lesser number of switching angles with proper initial guess. However, without proper initial guess and for large number of switching angles, the method fails to solve the system of equations. In this paper an improved numerical technique is proposed to solve the large number of harmonics elimination equations with any random initial guess. The method proposed also ensures multiple solutions of the simultaneous equations, hence gives more degree of freedom to operate converter at a particular modulation index. Simulation results are provided to validate the concept.