A Discontinuous Space Vector PWM Algorithm in abc Reference Frame for Multilevel Three-Phase Cascaded H-Bridge Voltage Source Inverters

Abstract

Previous space vector pulse-width modulation (SVPWM) methods for a multilevel three-phase voltage source inverter (VSI) have the problems including the computational complexity to identify the location of the reference voltage vector, the memory requirements of switching states and corresponding duty ratios, or no generalized switching pulse durations of switches. These problems are related to the level number, and they become critical at a high level number. In this paper, a discontinuous SVPWM algorithm in the abc reference frame is first proposed for a multilevel three-phase cascaded H-bridge (CHB) VSI. The L-level three-phase SVPWM problem is solved based on the two-level three-phase SVPWM one. Thus, the computational complexity to determine the nearest three switching states and corresponding duty ratios is independent of the level number. Furthermore, the proposed algorithm provides a systematic approach to calculate the switching pulse durations for a multilevel three-phase CHB VSI, and the approach can be extended to different multilevel three-phase VSIs. The proposed algorithm has no memory requirement and low computational complexity. It is verified by the simulation and experimental results for a five-level three-phase CHB VSI.