Dynamics of a Ferromagnetic Suspension System

A theoretical model for the study of nonlinear dynamics of a ferromagnetic suspension system is presented. The system analyzed consists of a single electromagnet, a suspended mass, and a control system to maintain the mass in a levitated position. The system, studied as a paradigm for a rotational magnetic bearing, can be described by a set of three first-order nonlinear ordinary differential equations. First, the well-known, open-loop instability is confirmed and then, it is shown that the closed-loop suspension system with a full-state feedback controller possesses interesting properties. In particular, it is shown that the system cannot be stable without velocity feedback and that the controller introduces an additional equilibrium point in the state space which is unstable.