Comparative study on heteropolar/homopolar magnetic bearings for high-speed rotating applications

Bearing technology must be supported to attain high-speed and high-efficiency rotating applications. Previous research focused on performance enhancement and optimization, rather than comparative studies among magnetic bearings. This study presents the design and comparison of five magnetic bearing types for high-speed rotating applications: an 8-pole conventional heteropolar, fork-type heteropolar, hybrid fork-type homopolar, and hybrid homopolar magnetic bearings. For quantitative evaluation, mechanical parameters were selected to ensure a uniform coil volume and current supply. The heteropolar magnetic bearings employed 35PN440 steel, whereas the homopolar magnetic bearings utilized pure solid iron. The bias currents were determined based on the respective material properties. The driving circuits were compared by comparing models with and without permanent magnets. The magnetic flux density was assessed at equilibrium and maximum control current, and the loss characteristics were evaluated at 30 000 rpm. Linear control regions were identified by analyzing the relationships between the electromagnetic force, current, and displacement. As a result, the most suitable magnetic bearing for high-speed rotating applications is proposed.