DETC2005-85454 DESIGN OF A COMBINED RADIAL AND AXIAL MAGNETIC BEARING

ABSTRACT This paper proposes a new compact active magnetic bearing(AMB) that has both radial and axial control functions in one bearing unit, which enables the removal of the large disk unlike conventional axial AMBs. The proposed AMB consists of four U-shaped cores circumferentially connected by yokes and two-layer windings for radial and axial controls; one is configured like a homopolar AMB, and the other is the same as that of a 4-pole heteropolar AMB. Since each winding can be used for radial control, the proposed system has two kinds of operating principle according to the radial control type. As for axial control action, it uses the Lorentz force generated by the interaction of the bias flux for radial control and the axial control flux. In this paper, the proposed structure, principle, and design process based on the magnetic flux analysis are introduced, and its feasibility is experimentally verified by using a simple PD controller with a feedforward loop to compensate a coupled effect. INTRODUCTION In general, active magnetic bearing(AMB) systems consist of a pair of radial AMBs and an axial AMB with a solid disk placed between two axial electromagnets. The disk for axial control often reveals a limitation on designing a compact AMB or a very high speed AMB. Thus, many researchers have attempted to develop various compact and simple-structured AMBs. One of them is a cone-shaped magnetic bearing that can simultaneously produce the axial and radial forces [1], [2], but its control algorithm becomes complicated due to the coupled dynamics between the axial and radial directions. As the most compact AMB, a miniaturized AMB with solid cores has also been tested for high-speed operatio