Sensorless control of magnetic levitation system using sliding mode controller

Magnetic levitation is a technique to suspend an object without any mechanical support. Position of the suspended object is generally detected by using Hall Effect or optical sensors. These sensors require additional mechanical fixtures making the system clumsy and less reliable. A magnetic levitation system without using such mechanical fixtures has been presented in this paper. Absence of additional fixtures to sense the position of the suspended object makes it very attractive for practical implementation. Position of the suspended object is sensed by measuring the change in inductance of the lifting magnet. Resonance method has been used for this purpose. Sliding mode control technique which is robust and easy to implement has been used. This technique also takes into account parameter variation and eliminates necessity of exact modeling. Simulation results show stabilization of the object even with wide variation in its mass. Chattering in the voltage applied to the lifting magnet has been reduced by introducing hysteresis in the control law.