An input switched multilevel inverter for open-end winding induction motor drive

This paper presents an input switched multilevel inverter topology for controlling a three-phase open-end winding induction motor drive. In this topology, DC link voltage obtained from a single voltage source is divided into `n´ equal steps, and a single pole multi-throw (SPMT) configuration is used to select any desired voltage level from these possible `n´ voltage levels. This is followed by H-bridge which can alternate the polarity of voltage obtained at its output and hence generating necessary ac voltage. One salient feature of this multilevel inverter drive system is that the number of switches used is greatly reduced compared with traditional neutral-point-clamped inverters and flying-capacitor inverters based systems. It is possible to obtain two additional voltage levels at the output by adding only two switching devices per phase. And the input switched inverter topology can be easily extended to obtain any desired voltage steps at the machine terminals. A hybrid modulation technique combining symmetrical sinusoidal PWM and traditional SPWM is also proposed. Circuit analysis, modulation technique and software simulation are illustrated with respect to a seven-level input switched inverter drive system.