Improved hexagram inverter for medium-voltage variable speed drive

The hexagram inverter is composed of six voltage source inverter (VSI) modules interconnected through the inductors, which are required to suppress the circulating current that resulted from the modular interconnection. Design of the inductor is a challenge, where the inductance should be large enough to suppress the circulating current but small enough to minimize additional voltage drop that affects the output voltage. This paper proposed using coupled inductors in between the connected VSI modules instead of individual ones. With the proposed structure, the circulating current can be maximally suppressed and the voltage drop introduced by the inductor can be minimized. In addition, by sharing the magnetic core, the cost and size of the inductors are reduced. Both simulation and experiments have been conducted to verify the proposed hexagram inverter structure.