Torque Improvement of Spoke-type Permanent Magnet Motor with Auxiliary Stator Using Harmonic Current Control Strategy

The spoke-type permanent magnet motor with auxiliary stator exhibits high torque performance owing to the flux focus effects. To further improve its torque density, this paper proposes a control method by using harmonic current strategy. Based on the theoretical analysis, a 3-D torque look-up table by dq-axis current and electrical angle is established with the aid of the finite element method (FEM). The maximum torque per ampere curve at each rotor position is identified and summarized to adequately indicate the relationship between torque and current amplitude of the motor. Through theoretical derivation, it is concluded that the minimum torque cost curve is the contour line of partial derivative T-e/partial derivative i(2), which can be employed to identify the harmonic current for torque density improvement. Compared to traditional strategies, the proposed control strategy can increase torque density of forward and reverse torque by 1.22% and 1.40%, respectively. The experimental results verify the analysis and simulation results, as well as prove the effectiveness of the proposed strategy.