Multilevel converter fed induction motor drive for industrial and traction drive

摘要

Recently, multilevel converters have attracted attention in medium-voltage and high-power applications due to reduced voltage stress on power semiconductor switches, reduced voltage harmonics, and electromagnetic interferences. For higher voltage and high-power applications, the switching frequency and device ratings are limited. Therefore, it is desirable to distribute the stress among the number of devices using a multilevel converter. There are three important multilevel topologies: the neutral point clamped (NPC) multilevel converter, flying-capacitor multilevel converter, and cascaded H-bridge multilevel converter. Research in the area of multilevel bridge converters has mostly concentrated on three-level NPC converters for medium voltage and high power drive applications. Theoretically, diode clamped topology with any number of levels can be visualized. But some of the problems like unbalanced voltages across capacitors, voltage clamping requirements, complexity of switching algorithm, circuit layouts, and packaging constraints have limited the number of levels in a practical multilevel converter to seven. The main focus of this article is to develop an experimental setup for graduate level research for a three-level NPC front-end ac-dc converter and a three-level NPC inverter that feeds the induction motor drive. By using this topology, the front end ac-dc converter can operate in utility friendly mode drawing sinusoidal input current at unity power factor while the induction motor drive is operated with closed-loop speed control having four-quadrant capability.