Optimization on Torque Ripple Performance in ISG Motors With Fractional Slot Distributed Windings and Rotor Notching

Abstract

The torque ripple of an electrical machine will affect the control accuracy and trigger vibration and noise in the system. Consider only the motor itself, the torque ripple is mainly caused by the cogging torque at no load, the harmonic component of the induced electromotive force, and the saturation of the magnetic fields in load operation. In this paper, a two-stage optimization approach is used to reduce torque ripple and cogging torque for an integrated starter and generator(ISG) machine. The first level of optimization mainly adopts the appropriate pole-slot combinations, and for a machine with an initial model of 6-pole/36-slot, it is optimized to 8-pole/36-slot, which significantly reduces the cogging torque and torque ripple. The second level of optimization is rotor notching, and the notch strategy is classified into three types, Q-axis notch, magnetic bridge notch(MB notch), and Q-axis and magnetic bridge notch combination(QMC notch), and the selection of each notching parameters is analyzed respectively. For the Q-axis notch, the parameter sweep method is mainly used to determine the parameters, and for MB notch and QMC notch, the non-dominated sorting genetic algorithm-II(NSGA-II) is used for multi-objective optimization to determine the parameters. Then torque performance and total harmonic distortion(THD) are analyzed for each design. Finally, the rotor strength was analyzed. Simulation results show that suitable pole-slot combinations can reduce the cogging torque and torque ripple to a greater extent. Selection of suitable rotor notching can improve the torque performance again to some extent, in which the QMC notch design is preferred and recommended.

Keywords

• Cogging torque
• interior permanent magnet synchronous motor (IPMSM)
• notch
• non-dominated sorting genetic algorithm-II (NSGA-II)
• torque ripple