Permanent magnet synchronous machines with fractional slot and concentrated winding configurations

Abstract

The permanent magnet synchronous machines with fractional slot and concentrated winding configuration have been steadily gaining traction in various applications in recent times. This is mainly driven by several advantages offered by this configuration such as high-torque density, outstanding efficiency, and easy and low-cost fabrication. The main focus of this thesis is dedicated to the investigation of three main topologies of fractional-slot and concentratedwinding permanent magnet synchronous machines specifically suited for particular applications. Additionally, the cogging torque and torque ripple reduction technique based on a novel axial pole pairing scheme in two different radial-flux permanent magnet synchronous machines with fractional-slot and concentratedwinding configuration are investigated. First, an axial flux permanent magnet segmented-armature-torus machine with laminated stator is proposed for in-wheel direct drive application. Both simplified analytical method and three-dimensional finite element analysis model accounting for anisotropic property of lamination are developed to analyze the machine performance. The predicted and experimental results are in good agreement and indicate that the proposed machine could deliver exciting and excellent performance. The impact of magnet segmentation on magnet eddy current losses in the prototype is carried out by the proposed three-dimensional finite element analysis model. The results show that the eddy current losses in the magnet could be effectively reduced by either circumferentially or radially segmenting the magnets. Furthermore, a magnet shaping scheme is employed and investigated to reduce the cogging torque and torque ripple of the prototype. This is validated using the three-dimensional finite element analysis model as well. Second, a coreless axial flux permanent magnet machine with circular magnets and coils is proposed as a generator for man-portable power platform. Approximate analytical and three-dimensional finite element analysis models are developed to analyze and optimize the electromagnetic performance of the machine. Comprehensive mechanical stress analysis has been carried out by threedimensional structural finite element analysis, which would ensure the rotor integrity at expected high rotational speed. The results from both three-dimensional finite element analysis and experiments have validated that the proposed prototype is a compact and efficient high speed generator with very simple and robust structure. Additionally, this structure offers simplified assembly and manufacturing processes utilizing off-the-shelf magnets. Third, a novel radial flux outer rotor permanent magnet flux switching machine is proposed for urban electric vehicle propulsion. Initial design based on the analytical sizing equations would lead to severe saturation and excessive magnet volumes in the machine and subsequently poor efficiency. An improved design is accomplished by optimizing the geometric parameters, which can significantly improve the machine efficiency and effectively reduce the overall magnet volumes. Magnet segmentations can be employed to further improve the machine performance. Finally, a novel axial pole pairing technique is proposed to reduce the cogging torque and torque ripple in radial flux fractional-slot and concentrated-winding permanent magnet synchronous machines. The implementation of the technique in outer rotor surface mounted permanent magnet synchronous machine shows that the cogging torque and torque ripple can be reduced very effectively with different magnet pairs. However, careful pair selection is of particular importance for compromise between cogging torque and torque ripple minimizations during the machine design stage. This technique is also employed to minimize the cogging torque in a permanent magnet flux switching integrated-stator-generator and it is compared with rotor step skewed technique. The estimated and experimental results show that the axial pole pairing technique can not mitigate the torque ripple of the machine as effectively as rotor step skewed approach although both the techniques could reduce the cogging torque to the same level.