Analysis and design of an ultra-high-speed slotless self-bearing permanent-magnet motor

Active magnetic bearings (AMB) enable contactless operation and can therefore be used for supporting rotors spinning at high speeds. However, the rotational speed in conventional reluctance-force-based AMB topologies is limited which is mainly due to high rotor losses and achievable force control bandwidths. In this paper, a prototype of a self-bearing motor designed for rotational speeds of up to 500 000 revolutions per minute (rpm) is presented. Due to the employed AMB, the motor can be operated in high-purity or vacuum environments. An analytical mechanical and electrical bearing model is introduced and verified by measurements. Furthermore, a bearing inverter system is designed and its controller performance is shown. Closed-loop system measurements of a spinning levitated rotor at 400 000 rpm verify the functionality of the overall system. To the authors knowledge, this is the world record speed for magnetically-levitated electrical drive systems.