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.