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 mu 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 mu controller over an optimized PD controller. Interestingly, the mu 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