Generation of multilevel voltage profile for torque ripple reduction of a 15 phase pole-phase modulated induction motor drive using two-level inverter structure

Pole phase modulation (PPM) of multiphase induction motor (MIM) drives increases the speed and torque range of MIMs used in high power propulsion and traction. Modulating the phase angle of voltage across stator windings which in turn adjusts the pole of MIMs to achieve wider speed and torque ranges is the basic principle of PPM. 15-phase PPM induction motor (PPMIM) drive gives 15-phase 4-pole, 5-phase 12-pole and 3-phase 20-pole mode of operations providing wider torque and speed ranges. Due to reduced space harmonics in the air gap because of high phase number, performance of the PPMIM drive under 4-pole mode of operation is good even with two-level inverter voltage excitation. In case of 5-phase 12-pole and 3-phase 20-pole modes of operation, space harmonics in the air gap increases due to reduction in phase number resulting increased torque pulsation and decrease in efficiency for two-level voltage excitation. Reducing the time harmonics by increasing the inverter voltage levels is one of the solutions to improve the performance of PPMIM drives for high pole modes. But employing conventional multilevel inverters for MIMs increases the device count, control complexity and cost of the drive system. In this paper an effective method to improve the performance of 15-phase PPMIM under high pole modes is presented. The equipotential phase coils (EPCs) forming the effective phase of 5 phase 12 pole and 3 phase 20 pole mode of operations are utilized to generate multilevel voltage across effective phases using carrier phase shifted pulse width modulation (PWM). The torque pulsations and efficiency of the PPMIM drive for two-level and multilevel voltage excitation using single carrier and multiple phase shifted carriers respectively are compared. The FEM model of 15 phase PPMIM is developed in Ansys Maxwell 2D and is co-simulated with a 15 leg two-level inverter in simplorer environment.