Magnetic levitation based on switched reluctance actuator

Abstract

For a high performance mechatronic system, magnetic levitation has many advantages. It is contact-free, and it can eliminate many mechanical components e.g., gears, guide, ball bearings, etc. On the operation side, magnetic levitation can reduce the mechanical alignment cost, the wear and tear, and maintenance cost. Therefore, investigations into contact-free mechatronic systems have been actively performed by worldwide researchers. Switched reluctance actuator is an electrical device in which the output force is produced by the tendency of its magnetic circuit to minimize the reluctance of excited winding. Switched reluctance actuator has the merits of simple structure, low cost and high reliability. Hence, the magnetic levitation system based on switched reluctance principle could be a potential candidate for mechatronic carrier systems. The magnetic levitation system based on switched reluctance actuator is hard to control due to high inertia and inherent nonlinear flux characteristics. For a multipoint levitation system, the coupling behavior will complicate the control algorithm of this multiple-input and multiple-output system. The ultimate objective of this project is to investigate and propose an effective control scheme for the multiple-input and multiple-output magnetic levitation system by using switched reluctance actuators. To achieve this target, the first step is to investigate and develop the magnetic levitation actuator and to explore the magnetic performance characteristics of this actuator. The principles of operation of the proposed magnetic levitation system with switched reluctance actuator are reviewed. Magnetic circuit analysis model, three-dimensional finite element analysis model and experimental implementation are applied to analyze electromagnetic force. The accuracy of the magnetic circuit analysis model is developed and further improved. Following the establishment of the switched reluctance magnetic levitation actuator, the next task is to model the magnetic levitation system. Both the single-input and single-output magnetic levitation system and the proposed multiple-input and multiple-output magnetic levitation system are modeled. These modeling reveal the open loop instability and coupling behavior of the proposed system. To simplify the control scheme of the overall system, a two-time scale method is implemented, and the magnetic levitation system can be divided into two reduced-order subsystems, electrical model and mechanical motion model. On basis of the reduced-order model, a sliding mode controller is approached for the single-input and single-output magnetic levitation system. The stability and the system characteristics of the controller are both analyzed. An observer based the sliding mode controller is developed to against disturbances and to improve the system performance. Finally, a control algorithm for the multiple-input and multiple-output magnetic levitation system is proposed. The coupling system is decoupled into three individually controllable subsystems by mathematical transformation. Following that, the sliding mode controller approached in single-input and single-output magnetic levitation system can be applied to these subsystems. This project has demonstrated that, through proper actuator design and control, multipoint magnetic levitation based on switched reluctance actuators could be an alternative to the present existing magnetic levitation methods.