SHE PWM for multilevel inverter using modified NR and pattern generation for wide range of solutions

Abstract

In medium voltage high power applications good quality waveform with low switching losses is more preferred. In this context, low switching frequency modulation techniques based on pre-computed PWM switching patterns is very useful because the generated harmonic content is known in advance and therefore can be optimized as much as possible. Among the different low switching frequency Pulse width modulation (PWM) techniques, the Selective harmonics elimination (SHE) modulation method is widely investigated and applied because of direct control over the harmonics spectrum. This paper proposes a method for obtaining multiple solutions for switching angles in wide range of operation while selectively eliminating specific harmonics by using modified Newton Raphson (NR) and pattern generation approach. This methodology leads to multiple solutions and provides more flexibility to operate power converter in a wide range of modulation. In this paper only exact solution for the low order harmonics elimination of a multilevel converter are reported at all modulation indices. Analytical and Simulation results prove the robustness and correctness of the proposed technique.