Nonlinear behaviour and control of active electromagnetic bearings

This paper investigates nonlinear behaviour and control of magnetic actuators used in electromagnetic bearings,via a high-speed rotor supported by ten electromagnetic actuators and subjected to unbalance and external forces. The actuators having forces proportional to the square of the electric control current and inversely proportional to the square of distance from shaft surface are controlled using a simple and feasible control strategy. The piece-wise control strategy used here has made the system adaptive to changes in both inputs and internal system parameters at the same time as the required energy is kept to a minimum. Fewer computational steps are required with this control strategy, and the use of an online digital computer results in higher shaft speeds and a better response to larger high-frequency disturbances. Finally, the authors show that the measurement of centrifugal forces and accelerations is not necessary to control the system, and that the bearing system can adapt to these forces.