Fuzzy logic based control of rotor motion in active magnetic bearings

Active magnetic bearings (AMB) are increasingly being used as an alternative to rolling element and fluid-film bearings in rotating machinery application. Stable operation of AMB can only he achieved via feedback control of which the most widely used controllers are of the linear PID type. Under extreme conditions, however, the dynamic response of the rotor in AMB becomes highly nonlinear. As a result, the linear controllers are no longer capable of suppressing or controlling the bifurcations of the rotor response. In order to suppress the non-linearity in AMB, a nonlinear control strategy is required. One of such strategies is the use of fuzzy logic based control approach. This paper aims to investigate and analyze the dynamical response of rotors in active magnetic bearings in AMB and presents the development and implementation of a fuzzy logic control strategy for suppressing the non-synchronous response in AMB. This control strategy is expected to stabilize the rotor-bearing system or to delay its onset of instability. Through modeling and simulation of the non-linear rotor response, it is found that for certain operating parameters, the rotor in AMB exhibits non-synchronous response (quasi periodic or chaotic). However, the use of fuzzy logic control has been able to eliminate the undesirable non-synchronous response and improve the rotor stability performance.