A novel hybrid inverter drive for AC motors capable of bypassing the voltage source inverter when operating at grid frequency

Abstract

Variable speed drives (VSDs) offer reduced power consumption for applications which allow operation at reduced motor speed. However, when continuous operation at the grid frequency is required, the VSD may become redundant, as it introduces conversion losses and electromagnetic interference (EMI), in contrast to grid-connected operation. It is hereby proposed to bypass the VSD for continuous operation at the grid frequency. This paper introduces a VSD, based on a two-level voltage source inverter (VSI), capable of transferring a motor load between grid- and inverter-connected operations, depending on the required motor speed. This paper presents a thorough analysis of the conditions under which the motor load may be transitioned from either operating mode. Thyristors are used as bypass devices. Simulation results for open and semiclosed transitions are presented, examining their impacts on the motor torque and stator currents.