Hexagram Inverter for Medium-Voltage Six-Phase Variable-Speed Drives

A new multilevel inverter - hexagram inverter is proposed for medium-voltage (MV) variable-speed-drive (VSD) applications, which is composed of six standard two-level voltage source inverter (VSI) modules interconnected through the inductors. With six AC terminals, it can be used for both three- and six-phase drives. This paper studies its six-phase applications. Compared to a same output power and voltage VSI, the proposed inverter has the current stress reduced to half and voltage stress reduced to one-third; whereas compared to a same output power and current VSI, the voltage stress is reduced to one-sixth. The other advantages of the new inverter include a modular structure resulting in easy construction and maintenance, no voltage unbalance problem, easy control with well-developed VSI control techniques, automatic and equal current and power sharing among the modules, and fewer components and lower dc energy storage requirements compared to the cascaded H-bridge (CHB) inverter. These eminent features make it a strong candidate for MV VSD applications.