Evaluation of the Torque in High-Speed PMSMs With a Shielding Cylinder and BLDC Control

Abstract

High-speed electric machines with permanent magnets are sometimes equipped with a shielding cylinder; a conductive sleeve that is wrapped around the magnets in order to reduce the rotor losses and/or retain the magnets. Despite the every increasing popularity of such high-speed permanent-magnet synchronous machines (PMSMs), there are still a lot of question regarding the effect of the shielding cylinder. Earlier work in literature evaluates how the shielding cylinder’s design affects the machine’s performance. However, that work assumes a sinusoidal current, hence neglects the stator current’s higher time-harmonic orders. Therefore, this paper aims at evaluating how different stator sources affect the way in which the shielding cylinder influences the torque production in high-speed PMSMs. The study is performed using a 2-D analytical subdomain model that accounts for slotting and the eddy current reaction field. Both current and voltage sources are considered. The torque is divided in two components, the classical torque due to interaction between the magnets and the stator currents and the torque due to interaction with the eddy currents in the shielding cylinder. This approach results in a better insight in the machine’s physics.