Air-gap and yoke flux density optimization for multiphase induction motor based on novel harmonic current injection method

This paper investigates a novel harmonic current injection method to optimize air-gap and yoke flux density distribution for multiphase motor simultaneously. The effect of harmonic currents on air-gap flux density and yoke flux density is analyzed as a whole. The proposed method fully makes use of multiple control freedoms, and the optimal coefficients for corresponding harmonic current are derived. Maintaining the same stator current density, a nine-phase induction motor improves torque density about 6.6% with the proposed method. A three-phase induction motor is designed to verify the effectiveness of multiphase motor with concentrated full-pitched winding. Furthermore, the torque density and efficiency for two motors are compared under various load condition. Finally, a multiphase variable speed drive system is constructed and the proposed method is validated by experiments.