A three-level inverter configuration for pole-phase modulated nine-phase induction motor drives with single DC link

This paper proposes a 3-level inverter scheme with a single dc source to enhance the performance of pole phase modulated multiphase induction motor drives (PPMMIM). Each phase of the traditional 9-0 4-pole induction motor (IM) has two series connected identical voltage profile coils (IVPC) with a span of two pole-pitches. These two IVPC's are disconnected and reconnected as two 9-phase star groups, which are excited with 9-0 2-level inverters separately. But these inverters are connected to the common-dc link. The dc-link requirement of the 9-0 IM drive is reduced by 6 times as compared with the traditional 3-0 IM drive. In high pole operation, PPMMIM drives supplies huge starting torque with reduced phase count, which increases the magnitude space harmonics in air gap. With the help of phase shifted carrier space-vector pulse width modulation (SVPWM) the proposed MLI scheme produces the multilevel voltage across the effective phase. The first center band harmonics in the effective voltage are cancelled because of the 180⁰ phase shifted references. In addition, the other center band harmonics are moved to the higher order of frequencies due to phase shifted carriers. This improvement in harmonic profile as well as multilevel voltage excitation improves the performance of the PPMMIM drive in 12-pole mode. In low pole mode, the dc-link voltage utilization (DLVU) of the MIM drive is enhanced by 15.4% with the help of third harmonic injected SVPWM. A 5hp 9-0 4-pole FEM model is designed in Ansys Maxwell 2-D for validating the proposed MLI configuration. This configuration is also verified by using laboratory prototype.