Reduction of the cogging torque is preferred during the design process of a permanent magnet (PM) synchronous machine (PMSM), especially in the low-speed traction applications. This article presents a dual-skew magnet technique to minimize the cogging torque in the axial-flux permanent-magnet (AFPM) motor with a yokeless and segmented armature (YASA). The theoretical expression of the cogging torque of the AFPM machine is deduced, and the advantages of the dual-skew magnet are verified by comparing with a sector shape magnet and a conventional skew magnet using the 3-D finite-element method (FEM). The simulation results show that, compared with the other two magnet topologies, the machine equipped with the dual-skew magnet shows its advantages in the reduction of cogging torque, torque ripple, and magnet eddy current loss.

Identification of the stator d-axis and q-axis inductances is essential for interior permanent magnet synchronous motor (IPMSM) sensorless control system. The signal injection method is an effective way to identify the inductance parameters, however, it requires the rotor position to ensure the accuracy of the injection reference position. To overcome the dependence on the rotor position, a sequence-pulse voltage signal injection method is presented. The matrix least-square fitting algorithm is utilized to fit the current responses for inductance identification. Based on the fitting method, the discrete standard orthogonal polynomial with look-up table is introduced to reduce the computation complexity. To reduce the disturbance of the injected signal to the rotor position during the identification process, a double-direction injection position trajectory planning is presented. In addition, the saturation effect on the identification method is also analyzed. The proposed method is verified via a 3.0 kW IPMSM motor drive platform. The identification results are compared with those measured by standard method and experiment results show that the proposed method can identify the inductance parameters with acceptable accuracy without obtaining rotor position information.

The yokeless and segmented armature axial flux machine is considered an excellent topology for electric vehicles application. However, its performance is severely limited by the stator cooling system. The heat pipe, as the small size, lightweight, but highly efficient passive phase-change cooling element, has been attracting more and more attention in the thermal management methods of electric motors. Therefore, the relationship between the thermal performance of the heat pipe with temperature is measured in detail through an experimental test platform in this paper. Further, a novel stator cooling structure that combines the heat pipe with the housing water-cooling method is introduced to improve the temperature distribution of the stator. Computational fluid dynamics (CFD) simulation verifies that the proposed cooling structure can accelerate the release of heat from the stator and reduce the temperature of the stator significantly.

In this paper, a novel High Power Density Permanent Magnet Synchronous Machine (HPDPMSM) is proposed. The flux-weakening ability and efficiency at high speed are improved by the proposed bypass-ribs added in the flux barriers. The working principle of the bypass-rib is analyzed and the effects of main parameters of the bypass-rib on the characteristics are investigated. The performances of the proposed HPDPMSM are analyzed and compared with that of the HPDPMSM without bypass-rib on 2D finite-element analysis (FEA), including the cogging torque, output torque, constant-power speed range, losses and efficiency. The results show that both HPDPMSMs generate comparable output torque and have the same maximum output power, while the proposed HPDPMSM has lower torque ripple, wider constant-power operation range and higher efficiency in the flux weakening operation region.

The temperature of axial flux motor components directly affects the performance of machine. The cooling design for the rotor is obviously difficult because of its inherent rotation characteristic. A rotor air-cooling enhanced method for axial flux machines with housing-cooling is proposed in this article. In order to improve the air-cooling performance of the rotor, tile-shaped fins are mounted to the inner wall of the housing taking into account the fluid flow characteristics of axial flux motors in a cavity. The impact of the key parameters on the thermal performance are investigated by the theoretical analysis and computational fluid dynamics. In addition, the thermal model of the tile-shaped fin is derived, and the thermal network of the rotor is constructed accordingly. Finally, two prototype motors are manufactured to evaluate the viability of the proposed approach. The results of theoretical and experimental studies show good agreement.