Minimizing the Circulation Current in Hexagram Medium-Voltage Variable-Speed Drive by Coupled Inductors

The hexagram inverter is composed of six voltage source inverter (VSI) modules interconnected to form a circle via the inductors, which are required to suppress the possible circulating current in the circle. However, the design of the inductors could be challenging, where the inductance should be large enough to suppress the circulating current and small enough to minimize the effect on the output voltage. This paper proposes the utilization of coupled inductors in between any two connected VSI modules instead of stand-alone ones to optimize the hexagram inverter performance. On the basis of this structure, the circulating current can be maximally suppressed by the magnetizing inductance of the coupled inductor, while in the meantime, the output voltage is minimally affected by the leakage inductance. By sharing the magnetic core, the cost and size of the inductors are also reduced. Simulation and a small-scale experiment have been conducted to verify the proposed hexagram inverter structure with the six-winding coupled inductors.