An Active Magnetic Bearing With Controllable Permanent-Magnet Bias Field

Permanent-magnet (PM) biased magnetic bearings use a magnet to produce the bias field rather than applying a bias current, thereby eliminating the associated electrical power losses and heat generation. In the existing PM-biased magnetic bearings, the PM materials NdFeB or SmCo are generally employed due to their superior properties. However, these PMs should be pre-magnetized, and the generated bias magnetic field cannot be adjusted, limiting the flexibility of the magnetic bearings. This article proposes a new type of PM-biased magnetic bearing that uses a low-coercivity AlNiCo magnet and equips a magnetization coil to magnetize the magnet in situ. As a result, the magnet can be post-magnetized to make the assembly process of the machines easier without the disturbance of magnetic force, and the bias field generated by the magnet can be actively controlled to improve the rotor iron losses and force characteristics of the magnetic bearing. Experiments on a prototype successfully verify the advantages of the presented magnetic bearing.