Five-Level Inverter Topology for Induction Motor Drives With Common-Mode Voltage Elimination in Complete Modulation Range

Common-mode voltage (CMV) generated by different topologies of the pulse width modulated (PWM) inverters causes shaft voltage, bearing current and ground leakage current in the induction motor (IM) drive system. Consequently the premature mechanical failure (fluting) of machine bearings and conducted electromagnetic interference (EMI) are observed in the multilevel PWM inverter fed IM drive systems. A five-level inverter topology with switching state combination selection strategy for PWM control is proposed for an IM drive for complete elimination of CMV in the entire operating range of the drive, including over-modulation. The proposed scheme is based on a dual five-level inverter fed open-end winding IM drive structure. Each individual five-level inverter of the proposed drive is formed by cascading a three-level neutral point clamped (NPC) inverter with two conventional two-level inverters. Hence, the proposed individual five-level inverter offers simple power-bus structure with less number of power diodes as compared to the conventional NPC five-level inverter. The proposed open-end winding IM drive structure requires nearly half the dc-link voltage and provides increased number of redundant switching state combinations as compared to a single five-level NPC inverter fed conventional IM drive. The proposed CMV elimination scheme is experimentally verified on a 1.5 kW openend winding IM drive