Study On System Configuration And PWM Algorithm For Open-End Winding Machine And Muti-leg Inverter

In recent years, a novel three-level inverter configuration has been gradually emerging. It utilizes two inverters to connect with both ends of the machine open-end windings, called dual-inverter structure for short. Its output is equivalent to that of the traditional three-level inverter. Moreover, it has such advantages as fewer switches, no neutral point unbalance, redundant voltage space vectors, and so on. Thus, It is very important to study the topology structure and control method of the dual-inverter and open-end winding machine system, and to find a simpler structure or more effective PWM modulation technology.In this paper, through the deep analysis of three common PWM methods for the single-supply dual-inverter (six-leg inverter), the six-leg inverter topology and the PWM techniques are evolved. The Common-Mode-Voltage-Free SVPWM is first introduced. According to the switching states of the two inverters, five-leg inverter, four-leg inverter and three-leg inverter systems are gradually obtained by topology evolution, which largely simplifies the drive structure. Secondly, the Alternate-Sub-Hexagon-Center PWM algorithm is elaborated, and evolved from two perspectives, respectively:common-mode-voltage elimination method and inverter switching mode. The evolved PWMs can reduce the switching frequency of each inverter by 50% while decrease the distortion of the current waveform more efficiently. Then, both the inverter topology and the Decoupled PWM control method are evolved so as to obtain a five-leg inverter system, which not only simplifies the structure but also eliminates the common-mode voltage. Finally, experiments were conducted on the evolved inverters and PWMs. And the pros and cons of the original systems and the evolved systems are discussed from the view of harmonic spectrum. Test results confirm the validity of the evolved systems as well as the correctness of theoretical analyses.