Abstract

Permanent magnet synchronous machines (PMSMs) with rare-earth magnets are widely used in the traction drives of electrical and hybrid electrical vehicles, as they can provide high efficiency and torque density. Due to the possibility of future shortage of rare-earth materials, it is essential for electric vehicle industry to find alternative magnet technologies that can provide a substitute for rare-earth PMSMs. Permanent magnet machines with Alnico magnets can theoretically provide torque densities comparable to rare-earth PMSMs, due to their high remnant flux density. However, these magnets are rarely used in the conventional designs of PMSMs, as they can be demagnetized by the armature field.
The thesis presents a novel design for permanent magnet machines with Alnico magnets. The proposed design can provide high air gap flux density at no-load, and the armature field at full load tends to enhance the magnet flux. Therefore, the machine can operate with high torque density even under severe loading conditions. The demagnetization characteristics of Alnico magnets are also utilized to achieve high efficiency at a wide speed range, as the magnet flux is reduced at high speeds by armature current pulses that dissipate negligible losses, thus avoiding the additional copper losses of the continuous flux weakening current in conventional rare-earth PMSMs.
The simulation of the demagnetization and magnetization dynamics of the proposed machine design requires considering the hysteresis characteristics of the permanent magnets. Therefore, finite element analysis (FEA) simulations for the designed machine are performed using a linearized hysteresis model for Alnico magnets. The thesis also aims to improve the design and modeling of electrical machines by developing computationally efficient methods for incorporating the hysteresis characteristics of electrical steel into electrical machine models.