Analysis and μ-based controller design for an electromagnetic suspension system

A SISO electromagnetic suspension system including an electromagnet, an iron ball, a position detector, and a current amplifier is built at the laboratory. It is inherently nonlinear and unstable. In this paper a controller is designed for the suspension system to regulate the position of the suspended ball around an equilibrium point. It is also required that the number of the suspended balls can be increased from one (0.533 kg) to three (1.6 kg), For mathematical modeling, the change of mass of the iron ball and the equilibrium points can be treated as structured uncertainties of the controlled plant. Then, mu-synthesis algorithm is applied for a robust controller design to achieve the requirement of robust stability and robust performance. In addition, a classical phase-lead controller and a quadratic optimal controller are also designed for performance comparison.