Experiment on Changeover Voltage Surge Suppression in Gradationally Controlled Voltage Inverter Model without Transformers for Maglev System

Abstract

The converter in the Yamanashi Maglev system, which has PWM inverters connected in series via output transformers, has some points to be improved. One is that the transformers are costly and require a large space the other is that a large filter is required to suppress the zero sequence current. In this paper, we propose a gradationally controlled voltage inverter without transformers for the Maglev system. It has one set of three-phase, 3-level inverters and three sets of 7-level, single-phase inverters, which are connected in series. It can output 21 gradational voltage levels and can suppress the zero-sequence voltage which causes the zero sequence current. We at first explain the principle, features, and expected problems of the inverter system. Then we demonstrate the generation of a gradationally controlled voltage with an experimental inverter model. Finally, we explain how to suppress the changeover voltage surge which occurs at the point when changing the level. We conclude that the gradationally controlled voltage inverter without transformers will be useful for the Maglev system.