Quantitative Power Quality and Characteristic Analysis of Multilevel Pulsewidth-Modulation Methods for Three-Level Neutral-Point-Clamped Medium-Voltage Industrial Drives

The inherent low switching frequency in medium-voltage alternating-current industrial drives presents power-quality and filter-design challenges. In this paper, four multilevel pulsewidth-modulation methods; phase disposition (PD), switching-loss minimization (SLM), and selective harmonic elimination (SHE) up to the 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 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 with the PD and SLM algorithms. Elimination of up to the 29th harmonic achieves the best harmonic performance without needing an output filter, at the expense that the losses are higher with a lower efficiency. Analytical and simulation results using the Piecewise Linear Electrical Circuit Simulation for the power-electronic circuits and MATLAB/Simulink for control systems are experimentally verified with a 1000-hp 4160-V neutral-point-clamped adjustable-speed-drive system that includes a 24-pulse front-end voltage source converter.