Performance improvement of a nine phase pole phase modulated induction motor drive

Pole phase modulated (PPM) multiphase induction motor (IM) drives for applications like ship propulsion starts with high pole mode of operation to provide high starting torque required and then switch over to low pole mode of operation for steady run with high speeds. The performance of the nine phase PPM IM drive in case of nine phase four pole operation is inherently good due to high phase number even with a two level inverter. In case of high pole mode of operation (3 phase 12 pole) of the PPM IM drive the torque ripple is not within the acceptable range of safe limits, which brings in the need of multilevel voltage excitation to achieve better performance. Conventional multilevel inverters for nine phase IM suffers with problems such as capacitor voltage balancing issues and considerably high device count. In case of three phase twelve pole operation of the PPM IM drive each phase voltage is the sum of voltage across the three equal voltage profile coils (EVPC). In This paper the advantage of EVPC is exploited to generate a multilevel voltage across each phase using phase shifted carrier PWM keeping the device count same as 2 level nine phase inverter. The effectiveness of the proposed scheme is shown by FEA simulation in ANSYS Maxwell and simplorer environment. Significant reduction in torque ripple magnitude and increase in torque ripple frequency is observed in case of 3 phase 12 pole operation.