On-line diagnosis of sensor faults in active magnetic bearing system equipped with built-in force transducers

Abstract

Active magnetic bearing(AMB) is an electromagnetic device which levitates the rotor without mechanical contact by using the controlled electromagnetic force. Since the attractive electromagnetic force inherently makes the system unstable, the feedback control loop is always required for stable levitation state. The AMB system has been widely used in industry due to its numerous advantages such as no mechanical friction and wear, no lubrication requirement, high peripheral speed, low energy consumption, high precision operation, adjustable stiffness and damping, continuous operating condition monitoring, etc. Of course, there are also drawbacks of AMB system such as high production cost and low reliability which currently draw much attention among many researchers. In particular, AMB, a new high technology product, needs extensive improvement in reliability for wide and safe field application. This requirement can be met by improving the individual reliability of each component or by introducing an intelligent system capable of fault detection and diagnosis(FDD). For this purpose, basically, the following two conditions should be pre-satisfied: the accurate identification of system parameters and dynamic characteristics, and the acquirement of redundancy. This work focuses on the development of the FDD scheme for sensor faults in an AMB system which utilizes the sensor redundancy. The AMB system, which is equipped with built-in force transducers, is developed in the laboratory. The force transducers directly measure in-plane electromagnetic forces generated by each radial magnetic bearings, which enables us to use the redundant information such as rotor position, magnetic force, and control current, for the parameter identification and the FDD process. In this work, the design procedure of the AMB system is described, and through the magnetic circuit analysis and the modeling of each components, the equation of motion for a rigid rotor-AMB system is derived. Co...