Dual-Inverter-Fed Six-Phase Open-End Winding Symmetrical and Asymmetrical Motor Drives Based on a Nine-Switch Converter With a Single DC Supply

Abstract

Six-phase motors provide substantial benefits in applications that require high power density, high reliability and fault tolerance, smooth torque, high efficiency and enhanced control capabilities. An important consideration related to these motors is the necessity for a six-phase ac drive, which commonly has the form of a dual two-level inverter. Furthermore, open-winding configurations employing a single or two isolated dc supplies have been proposed, offering advantages such as higher dc-link voltage utilization, improved reliability and fault tolerance. For six-phase motors, however, these solutions require four two-level inverters, and are thus characterized by a high number of switches. This work presents a study of a dual converter with a single DC voltage source and a reduced number of switches. To achieve this reduction, the proposed solution is based on a dual two-level nine-switch converter. A study of the application of this converter to both symmetrical and asymmetrical six-phase motors is presented. The analysis quantifies the limitations on the fundamental voltage applied to the motor windings as a function of the electrical angle displacement of the two motor windings. These limits are derived for different modulation strategies, highlighting that a proposed discontinuous modulation scheme can achieve maximum dc-bus voltage utilization for both symmetrical and asymmetrical six-phase motors. The proposed solution is validated through simulations in MATLAB/Simulink and tested via an experimental laboratory setup. The results confirm the theoretical predictions and demonstrate the agreement between the simulation and experimental results.