Quantitative power quality and characteristic analysis of multilevel pulse width modulation methods in medium voltage high power industrial drives

The inherent low switching frequency in medium voltage (MV) alternating current (AC) industrial drives presents power quality and filter design challenges. In this paper, four multilevel pulse width modulation (PWM) methods: Phase Disposition (PD), Switching Loss Minimization (SLM), Selective Harmonic Elimination (SHE) up to 17th and 29th harmonics respectively are considered. The characteristics of long cable effects on common mode voltage (CMV) and differential mode voltage (DMV), inverter losses and efficiency, induction machine (IM) voltage and current harmonics are analyzed. Very little has been published in these quantitative comparisons. It is shown that the SHE method has reduced CMV as compared to the PD and SLM algorithms. Up to 29th harmonic elimination achieves the best harmonics performance without needing an output filter, at the expense that the losses are higher with a lower efficiency. Analytical and simulation results using PLECS for the power electronics circuits and Matlab/Simulink for control systems are verified experimentally with a 1000hp, 4160V neutral point clamped (NPC) adjustable-speed drive (ASD) system that includes a 24-pulse front-end voltage source converter.