Space harmonic cancellation in a dual three-phase SPM machine with star-delta windings

This paper proposes a dual 3-phase SPM machine with star-delta windings. The machine is based on the widely adopted 12s/10p configuration and employs a number of methods to suppress the two largest core loss causing MMF harmonics. Firstly, stator shifting is used to reduce the 7th order harmonic, which is then completely suppressed through the use of a second 3-phase converter operating at a 15° phase shift with regard to the first one. Secondly, each of the winding sets employs 3-phase star-delta winding that are able to completely cancel the 1st order MMF harmonic. Additionally, these methods increase the amplitude of the torque producing harmonic and so yield a machine with better torque performance than a conventional 3-phase machine. Analytical modelling is used to demonstrate the cumulative impact on winding MMF harmonics. FEA is then used to validate the analytical predictions and to investigate other machine performance. The proposed machine demonstrates comparable average torque and efficiency to a 12-slot dual 3-phase machine, but offers a substantial reduction in torque ripple and PM eddy current losses. This helps improve the machine performance and reduce the risk of thermal demagnetization. A prototype machine has been manufactured and EMF and static torque measurements validate the expected performance of the proposed machine

Quantitative Comparisons of Outer-Rotor Permanent Magnet Machines of Different Structures/Phases for In-Wheel Electrical Vehicle Application

As one of the key components, low-speed direct-drive in-wheel machines with high compact volume and high torque density are important for the traction system of electric vehicles (EVs). This paper introduces four different types of outer-rotor permanent magnet motors for EVs, including one five-phase SPM machine, one three-phase IPM machine with V-shaped PMs, one seven-phase axial flux machine (AFM) of sandwich structure and finally one hybrid flux (radial and axial) machine with a third rotor with V-shaped PMs added to the AFM. Firstly, the design criteria and basic operation principle are compared and discussed. Then, the key properties are analyzed using the Finite Element Method (FEM). The electromagnetic properties of the four fractional slot tooth concentrated winding in-wheel motors with similar dimensions are quantitatively compared, including air-gap flux density, electromotive force, field weakening capability, torque density, losses, and fault tolerant capability. The results show that the multi-phase motors have high torque density and high fault tolerance and are suitable for direct drive applications in EVs.This research was funded by National Natural Science Foundation of China, grant number 52177052, and by the Natural Science Foundation of Shandong Province, grant number ZR2020ME207