A robust control of a magnetic suspension system with a flexible rail

This paper presents a robust control design for a magnetic suspension system which has strong nonlinearity, open-loop unstable characteristics, and parameter variations. The target plant to be controlled consists of a U-core electromagnet and a flexible rail. We describe the test rig and formulate the mathematical model and then we set up a control problem as the mixed sensitivity problem where the augmented plant is constructed with frequency weighting functions and the feedback controller is designed by using the H_∞ controller. The effectiveness of the designed controller is validated using several simulations. These results show that the magnetic suspension system is robustly stable against disturbance and gives the well-damped tracking performance for the external input signal