Nonlinear control for a large air-gap magnetic bearing system

Active magnetic bearings are increasingly being utilized in rotating machinery applications as an alternative to the conventional rolling-element and fluid-film bearing types. In this paper three control schemes for a large air-gap magnetic bearing system are described. In the large air-gap situation, the magnetic bearing system operates in highly nonlinear regimes .The non-linearity in this system is due to the relationship between the forces generated in the electromagnetic actuator and the coil current and the air gap between the rotor and the stator. In most practical applications, The PID controller is utilized to ensure stable operation of the rotating machinery. However, The PID controller becomes not effective enough when the machine operates in highly nonlinear regimes. So this paper develops a fuzzy logic strategy and sliding mode to improve the performance of the magnetic bearing system operating in nonlinear regimes. The considered controller design procedures are PD controller, Fuzzy logic strategy, and sliding mode. For all three schemes simulations are presented in order to make a comparison. Compared to the PD controller, the nonlinear control schemes give better performance.