Three-Pole Magnetic Bearing Design and Actuation

The three-pole magnetic bearing has recently gained interest within the magnetic suspension research community due to its simple structure that relies on only three coils and ability to be operated by three-phase power converters. However, the threepole bearing is substantially more complicated to control. Control strategies based on linearized current models result in parasitic coupling between x and y radial forces, yielding significant force vector errors. Research initiatives have developed distinct threepole geometries with varying capabilities and operating principles. This article reviews the various research initiatives on the threepole bearing, develops a generalized framework for considering the forces of any three-pole bearing configuration, exercises this framework to provide insights into fundamental design topology choices, and proposes a method to calculate exact control currents and an optimal bias field. This article shows that using the exact control current calculations with the proposed optimal bias field yields a force density improvement of up to 15.5% while requiring 23.4% fewer ampere turns as compared to using conventional bias levels. Experimental validation of the force calculation framework is provided.