Comparison of Stability Criteria for Rotor Levitated by Active Magnetic Bearing

In this paper, a phase margin, a gain margin, a sensitivity function, a maximum singular value of sensitivity function matrix and a damping ratio are taken up as indices which evaluate the stability margin of a rotor levitated by active magnetic bearings. The definition of the stability margin in this research is how far away the gain margin, the phase margin and the reciprocal number of the sensitivity function are from the critical point (-1 ,j0) in a polar plot. The stability margin distance is proposed to unify above-mentioned indices. We have estimated stability of a rotor-AMB system by these five indices and investigated relations among the indices.