High-power regenerative cascaded multicell converter with multilevel input and output

Abstract

Cascaded multicell converter is proved to be an effective solution for medium voltage high power drives. Three-phase diode bridge rectifiers with complex transformer configuration are normally used in this converter, which do not have regenerative capability. Three-phase or single-phase pulsewidth-modulated (PWM) rectifiers are used at the front end to achieve regenerative capability and input power factor controllability. However, the semiconductor devices are operated at high switching frequency due to two level voltage operation of these rectifiers. The single-phase PWM rectifier requires less number of switches and current sensors than the three-phase configuration. However, in this configuration, lower order harmonic currents circulate among the power cells through transformers; though these are absent in source currents. In this paper, a new configuration with single phase PWM rectifier based power cells is proposed to achieve multilevel voltage operation at both the input and output sides. Hence, the semiconductor devices of the rectifiers can also be operated at low switching frequency to draw quality source currents. Moreover, the lower order harmonic currents are also absent among the power cells. Analysis and simulation results are presented to confirm the effectiveness of the converter.