A hybrid multilevel inverter scheme for induction motor drives and grid-tied applications using a single DC-link

This paper proposes a hybrid seventeen-level induction motor drive with a single DC-link fed from a five-level active front-end converter connected to the utility grid. The five-level active front-end draws power from the grid at unity power factor and feeds a seventeen level induction motor drive. Both the grid side inverter (five-level) and the load side inverter (seventeen-level) are realized by cascading a three-level flying capacitor inverter with floating capacitor H-bridges. The voltages of the floating capacitors are controlled by switching through the redundant states. The capacitor voltage is regulated for all power factors irrespective of current direction. The main advantage of the proposed scheme is that, both front-end converter and the induction motor drive use a single DC-bus which enables multiple sources to interact easily with the proposed system. In addition to that, the proposed system can be operated in all four quadrants which enables bi-directional power flow. As an advantage, this system can operate at full power with reduced number of levels even when some devices of the H-bridges fail. This improves performance of the system without compromising on the reliability of the overall system. The performance of the drive for various operations has been verified experimentally.