Identification and mixed-sensitivity H? control of permanent magnet biased axial magnetic bearing with multiple air gaps

Due to the solid cores, eddy currents have significant influence on the dynamic performance of permanent magnet biased axial magnetic bearing (MB) with multiple air gaps. In this paper, the dynamic current factor is identified as a 3rd-order transfer function while the dynamic displacement factor is identified as a 2nd-order transfer function based on the results obtained by the finite element method (FEM), and the model uncertainty is determined by the closed-loop system test. The method of designing mixed-sensitivity H_∞ controller for the axial MB is analyzed. The designed H_∞ controller is proved to be effective by the experimental results. It has higher steady-state accuracy and much better high-frequency noise attenuation capability than the PID controller.