Modelling and effective controlling of radial electromagnetic bearings

Usually, it is not easy to develop a general control method for a given system but, by contrast, new algorithms are being developed every day. The aim of this paper is to show that some solutions are better than a commonly used approach. The considered system is nonlinear; consequently, a linearized model is diverse at some operational points. Therefore, an adaptive position controller of the active magnetic bearing may provide better results than a position controller designed for only one operating point. The main topic of the article deals with radial electromagnetic bearing (REB) control system design. The operating principles of electromagnetic levitation of a suspension with cylindrical shape are described. Furthermore, the nonlinear mathematical model of the REB and its linearization at an operating point is presented. The following part of the article is dedicated to control loop design. The parameters of the PI current controller and PID position controller are derived from the linearized REB model using the pole placement method. In addition, an adaptive PID position controller is designed with the previously mentioned method. The controller comprises a variation of partial gains depending on the actual position. Finally, results are obtained from simulations in Matlab Simulink.