Analysis of Fractional Slot and Vernier Permanent Magnet Synchronous Machines

Fractional slot (FS) vernier permanent magnet (PM) synchronous machines (VPMSMs) offer higher torque/power output capability under rated-load conditions. In particular, a compact structure and high torque/power density can be achieved when combined with concentrated winding (CW), consequent pole (CP) rotor, and multi-tooth stator structures. This thesis systematically investigates the effects of end windings, rotor topologies (north-south pole (NSP) and CP), and multi-tooth stator structures on the electromagnetic performance, unipolar end leakage flux caused by the CP structure, asymmetric PM loss and temperature distributions, and corresponding hotspot locations in conventional FS PMSMs and FS VPMSMs.
The electromagnetic performance, e.g., torque, torque density, power factor, etc. under various machine design optimization scenarios have been investigated and compared for SPMSMs with different slot/pole number combinations and rotor topologies (NSP and CP), accounting for the effects of end windings, coil pitches, and iron loss under different speeds.
Since unbalanced magnetic circuits in the north and south poles of the CP structure lead to unipolar end leakage flux, a simple and effective composite rotor, consisting of a non-magnetic shaft and a non-magnetic ring inside the rotor core (which could be integrated into a single shaft), is proposed to reduce the end leakage without sacrificing torque capability. The proposed structure can significantly mitigate the adverse effects of end leakage.
To further enhance torque and power densities, the FSCW is combined with the multi-tooth stator. The effect of multi-tooth numbers on the electromagnetic performances of NSP and CP VPMSMs is investigated and compared. The optimal multi-tooth number, in terms of torque characteristics, PM utilization, efficiency, and unipolar end leakage, is determined.
A finite element analysis (FEA) based harmonic restoration method is utilized to evaluate and quantify the asymmetric PM eddy current loss density and temperature distributions in SPMSMs which are found to be caused by the interaction between the armature reaction and PM fields. The resultant PM local hotspots are also investigated. Furthermore, the effect of armature reaction on asymmetric PM eddy current loss and temperature distributions in IPMSMs is also investigated and compared with SPMSMs.
All investigations have been carried out by electromagnetic and thermal FEA simulations and experimental verification.