Performance Enhancement of PPMIM Drives by using 3 Three-Phase Four-Leg Inverters

In this paper, a multilevel inverter (MLI) scheme is proposed for 9-phase pole phase modulated induction motor (PPMIM) drives. The proposed inverter scheme is realized with the help of 3 three-phase four-leg inverters. In 3-phase 12-pole mode (3PH-I2PO), the proposed MLI supplies a 3-level voltage for each phase winding of the PPMIM drive with an improved harmonic profile. This will minimize the amplitude of spatial harmonics in the airgap MMF, which results in better torque ripple in 3PH-I2PO operation. In this mode, for getting the same performance the PPMIM drive in w.r.t torque ripple the conventional 3-level 9-phase MLI's requires 40 switches, while the proposed MLI requires only 24 switches, which means the switch count is reduced by 40%. On the other hand, the phase windings of the 9-phase PPMIM drive are rearranged into 3 sets of three phase winding groups, where each phase group has three balanced 120⁰ phase displaced windings. This phase grouping will give the flexibility to use the 3-phase space vector pulse width modulation (SVPWM) that enhances the linear modulation of the 9-phase PPMIM drives by 15.4% in 9-phase 4-pole mode (9PH-4PO). The 4^th leg present in each three-phase four-leg inverter is used effectively for denying the circulating currents in phase windings in 9PH-4PO operation. The proposed MLI scheme is validated with the Ansys Maxwell FEM electromagnetic tool on a 5hp 9-phase PPMIM drive.