Design, analysis and application of magnetless doubly salient machines

Abstract

Owing to growing concerns on energy utilization and environmental protection, research on electric vehicle (EV) and wind power generation has drawn much attention in the past few decades. As a key component of these applications, the development of electric machines has become a hot research topic since the last century. While the permanent-magnet (PM) brushless machines have dominated the industrial and domestic markets for many years due to their outstanding performances when compared to their counterparts, the manufacturing costs of the PM machines have tremendously increased lately as a result of virtual market monopoly and fluctuating supply of PM materials. Therefore, with the absence of PM materials, the advanced magnetless doubly salient brushless machines that provide great cost-effectiveness have become more popular recently.

Without the need to install high-energy-density PM materials, magnetless doubly salient machines undoubtedly suffer from relatively lower torque densities when compared to their PM counterparts. To resolve this problem, the development of torque improving techniques has become an interesting research topic for the magnetless machines. On the other hand, unlike the PM machines whose magnetic fluxes are uncontrollable, the advanced magnetless machines can utilize its independent DC-field excitation for flux regulation. Hence, the operating ranges of the magnetless machines can be effectively extended.

The purpose of this thesis is to investigate the characteristics of existing magnetless doubly salient machines, analyze their design philosophies, and propose new topologies for various applications. Firstly, the background of magnetless machines and previous works conducted by other researchers are introduced. Based on the study of the existing works, the upcoming trend and the potential development are also reviewed. Secondly, the torque improving structures, namely the multi-tooth structure, the double-rotor (DR) structure, the axial-field (AF) structure, and the flux-reversal (FR) structure that are purposely implemented into the magnetless machines are discussed. Next, the idea to incorporate the design philosophies of the two different machines to form new dual-mode machines is covered. With the reconfiguration of winding arrangement and the support from controllable DC-field excitation, the proposed machines can further extend their operating range to fulfill extreme conditions required by the applications of EV and wind energy harvesting. Finally, all the key performances of the proposed machines are thoroughly analyzed by the finite element method (FEM), while the experimental setups have also been developed to verify the proposed concepts.