Bearing Currents and Shaft Voltage Reduction in Dual-Inverter-Fed Open-End Winding Induction Motor With Reduced CMV PWM Methods

Exploiting the rich switching redundancies of the dual inverter, new hybrid pulsewidth-modulation (PWM) switching methods are proposed in this paper using the degree of freedom of operating the individual inverters independently, in addition to exercising the degree of freedom of controlling the switching action of the individual legs independently. Two voltage entities, namely, common-mode voltage (CMV) and differential-mode voltage are identified in the dual inverter, and all hybrid PWMs are envisaged aimed at reducing and also eliminating the CMV in it. The effects of such attempts on motor shaft voltage and also the motor bearing currents are presented in detail. Furthermore, bearing current profiles of an open-end winding induction motor are also presented with both conventional and hybrid PWMs proposed in this paper. Electric discharge machining discharge currents are completely eliminated with the use of all hybrid PWM methods proposed in this paper. In addition, implications of completely eliminating the CMV are also presented in this paper. All hybrid PWMs proposed in this paper are first simulated using MATLAB and are experimentally verified on a dual two-level inverter feeding a 1.1-kW 415-V 3-φ open-end winding induction motor drive.