Spoke-type Interior Permanent Magnet Machines Research Articles

A General Pattern-Based Design Optimization for Asymmetric Spoke-Type Interior PM Machines

A novel asymmetric spoke-type interior permanent magnet (AS-IPM) machine is proposed in this paper. It utilizes the magnetic-field-shifting (MFS) effect to improve the torque performance, which achieves a high utilization ratio of both permanent magnet (PM) torque and reluctance torque. In addition, a general pattern of rotor topologies is proposed to represent all possible machine structures. Various rotor structures can be obtained by changing the design parameters of the general pattern. A non-dominated sorting genetic algorithm II (NSGA-II) is adopted to automatically search for optimal rotor configurations. With the aid of the optimization program, an asymmetric spoke-type rotor structure with improved performance is obtained. To showcase the advantages of the proposed machine, the electromagnetic performance is compared between a conventional spoke-type interior permanent magnet (S-IPM) machine and a proposed AS-IPM machine. The finite-element simulation results show that the optimal design of the AS-IPM performs a 7.7% higher output torque ripple due to the MFS effect while the total PM volume remains the same. Meanwhile, the torque ripple of the proposed structure is significantly reduced by 82.1%.

Semi-Analytical Calculation of the Unsaturated Magnetic Field Distribution of a Slotted Spoke-Type Interior Permanent Magnet Machine With Conformal Mapping Method

The performances of an electric machine are closely related to magnetic field, and the magnetic field calculation is the basic work of machine design and optimization. In slotted spoke-type interior permanent magnet (IPM) machines, the analytical calculation of magnetic field is complicated because the boundary of machine is difficult to model. Therefore, this article introduces a conformal mapping (CM) method to calculate the magnetic field semi-analytically. First, the interior magnet is transformed into the surface-mounted magnet to reduce the complexity of boundary conditions. The air-gap magnetic field of the slotless spoke-type IPM machine is calculated by using the boundary conditions of the transformed surface-mounted permanent magnet machine. Then, based on the magnetic field of the slotless air gap, the magnetic fields of the slotted air gap and teeth are also calculated by the CM method. All the semi-analytically calculated magnetic fields are directly verified by the FEM simulation and indirectly verified by the comparison of torque and back EMF. In addition, the comparison of computation time between the semi-analytical method and the FEM shows that the semi-analytical method is time-saving.

A Novel Spoke-Type Asymmetric Rotor Interior Permanent Magnet Machine

This article proposes a novel spoke-type asymmetric interior permanent magnet (AIPM) rotor topology that employs an additional asymmetric flux barrier in each pole of interior permanent magnet (IPM) synchronous machines for torque density enhancement and torque pulsating suppression without introducing any extra cost. The proposed AIPM-I machine, an existing spoke-type AIPM-II machine with asymmetric rotor profile, and a conventional spoke-type IPM machine are designed and optimized with the same 12-slot/8-pole stator with nonoverlapping windings as well as the same rotor diameter and PM dimensions. The effect of asymmetric flux barrier dimensions on the proposed AIPM-I machine is investigated with particular emphasis on torque characteristics. The electromagnetic performance and rotor mechanical strength of final optimal designs of three machines are compared. It confirms that the proposed AIPM-I machine can achieve significant torque enhancement and torque ripple reduction across the wide current range while also showing significantly smaller cogging torque at open-circuit condition, compared with both existing AIPM-II and conventional IPM machines. Finally, a prototype of the proposed AIPM-I machine has been manufactured and measured for validation.

A Spoke-Type IPM Machine With Novel Alternate Airspace Barriers and Reduction of Unipolar Leakage Flux by Step-Staggered Rotor

This paper proposes a spoke-type interior permanent magnet (IPM) machine with novel alternate airspace barriers, through which higher torque capability and better manufacturability can be obtained, without remarkable deterioration in mechanical strength. Further, the influence of end leakage flux in the novel IPM design is investigated by three-dimensional finite element method, including the leakage flux characteristics and torque capability. Furthermore, a step-staggered rotor is proposed to reduce the unipolar leakage flux and magnetization of the end shaft. As an extension, unipolar leakage flux is further investigated in consequent-pole PM machines, as well as the validity of step-staggered method. Finally, prototypes are fabricated and tested to verify the foregoing analyses, including the magnetic field at the end shaft and the output capability.