Bidirectional magnetic bearing with fault-tolerant capability

A fault tolerant current distribution scheme is presented for a bidirectional magnetic bearing with reduced eddy currents and cross coupled stiffness. The bearing continues to function normally even though one coil among four radial coils and on coil of two axial coils fail. The dynamic properties and load capacity remain unchanged for the suggested fault tolerant control scheme at the cost of additional hardware such as a decoupling choke, additional DSP channels, and power amplifiers. Novel improvements to reduce flux coupling between the radial and axial plane, lower eddy current loss, increase the current stiffness-inductance ratio are presented. A one-dimensional circuit that represents the bidirectional bearing is utilized to obtain the optimal bearing parameters such as the radial pole face area, number of coil turns and permanent magnet size. Three dimensional finite element models were also utilized. Nonlinear or anisotropic properties were assigned to the solid components and stacked laminates. Analysis with these models yielded gap flux densities, three by three current and position stiffness matrices, and insight into eddy current generation. The results identified advantages of the fault tolerant scheme and bidirectional bearing improvements relative to conventional magnetic suspension.