Efficiency Optimisation of Slotless Magnetic Bearing Machines

Efficiency is one of the key performance indexes in the design of electric motors. When considering fully active magnetic bearing machines, this aspect gain further relevance due to the necessity of actively controlling all the remaining degrees of freedom of the rotor in addition to its rotation. This article presents a strategy for efficiency maximisation of rotating machinery featuring slotless active magnetic bearings and motor. The efficiency optimisation maximises the motor and bearing constants, allowing the combined minimisation of losses and maximisation of the generated forces and torques. Due to the inherently complexity of active magnetic bearings, where multiple actuators are required for controlling different degrees of freedom of the rotor, a general optimisation procedure is proposed allowing a combined optimisation of several actuators. This approach is executed and validated using a 50-W and 20-krpm fully active magnetic bearing motor designed for space applications, resulting in a manufactured system featuring an efficiency increase between 33% and 58% with respect to the original machine.