Rotor compliance minimization via μ-control of active magnetic bearings

Many important problems in the control of rotating machinery with active magnetic bearings (AMBs) concern the minimization of the dynamic compliance of the rotor at a single or several shaft locations which typically do not correspond to those of a sensor or actuator. Experimental results are presented which demonstrate that controller design problems of this type can be successfully handled via μ synthesis. Herein, the problem of minimizing the peak dynamic compliance at the midspan of a rotor test rig is examined. A significant improvement in performance is obtained by a multivariable μ controller over an optimized PD controller. Interestingly, the μ controller obtained is unstable. Careful attention is given to developing an accurate system model, an important aspect of which is modeling the nonlaminated magnetic actuators used