Design and Analysis of Bearingless Synchronous Reluctance Machines

A doctoral dissertation completed for the degree of Doctor of Science (Technology) to be defended, with the permission of the Aalto University School of Electrical Engineering, Remote connection link https://aalto.zoom.us/j/63847391102 , on 16 October 2020 at 12 noon.A bearingless machine is a special type of electrical machine where the mechanism to levitate the rotor is integrated into the machine design. This thesis focuses on modelling and analysing different electromechanical behaviours of bearingless synchronous reluctance machines. Three models have been developed for different computational requirements, which include one finite element model, one reduced-order model and one analytical model. The models yield reasonably accurate results which are subsequently verified by the experimental results from a prototyped machine. It is found that the levitation force generation influences the iron losses of the machine, especially the hysteresis component. The vibration characteristics of the machine are also influenced by the levitation force production. Using numerical simulations, it is shown that the vibration components can be used to track the rotor displacement from the centre of the stator. The proposed analytical model clearly explains the variations in the inductance components of the machine's windings with the rotor's displacement. A novel algorithm has been proposed for the reduced-order model since the snapshot matrix selection requires additional consideration due to the complexities raised from the levitation force production. The levitation force ripple appears to be a major concern due to the properties of the reluctance rotor. The force harmonics are modelled with a novel method and an indexing technique which improve the understanding of the forces produced by the spatial harmonics of the magnetic flux density. Different reluctance rotor designs are investigated showing that a design compromise lies between maximising average torque, levitation force and minimising their corresponding ripple