Fundamentals of magnetic bearings

Abstract

Active magnetic bearings (AMBs) are non-contact bearings for rotating machines. A pair of electromagnets acting at opposite sides of the rotor balance the attractive magnetic forces in order to center the rotor in the control axis. Some fundamental concepts and terminologies that are needed for describing the operation and modeling of active magnetic bearings are introduced in this chapter. A simplified model of the AMB force is derived to study the interaction between the electromagnetic actuators and the rotor target. A linear variation of this model is commonly used in the design of rotor levitation controllers, and it is also presented in this chapter. Additionally, we discuss common AMB losses, such as flux leakage, eddy current, and hysteresis, which limit the maximum performance of the bearings. We conclude the chapter with a review of the different AMB levitation control methods that are found in the literature, including both classical and modern control methods.