DESIGNING ASPECTS OF TIME VARYING SLIDING MODE CONTROL AND CONVENTIONAL SLIDING MODE CONTROL FOR MAGNETIC LEVITATION SYSTEM

Abstract

The thesis covers the basic idea, mathematical and design features of conventional sliding mode control which is a technique to make any linear or nonlinear system unaffected to parametric uncertainty and external disturbances. It is shown that the main advantages of sliding mode control are order reduction, disturbance rejection and insensitive to parameter variations. The scheme of suppressing chattering is also explained. The main streamline of the study is the sliding surface design for the system. Since there is no systematic way of designing sliding surfaces for nonlinear systems, a time varying sliding surface is designed such that its parameters are determined in a linear and time varying manner to cope with the nonlinearities of the system. The linear, time-varying sliding surface is designed such that the system state is on the sliding surface from the start of the motion without reaching phase, thereby increasing the toughness of the system. The proposed method is then real time implemented on magnetic levitation system. Position control of a magnetic levitation system is one of the most fascinating and standard difficulties for control engineering. The time varying sliding mode controller is been proved capable of controlling the position of a steel ball floating in the air. A comparison of designed methods against conventional linear sliding mode controller is made through simulations. Simulation results have shown that the designed method enhanced the system performance, providing reductions in the reaching and settling times, and the proposed method has confirmed more robustness to disturbances and parameter discrepancies compared to its counterpart.