Smooth voltage controller and observer for a three-pole active magnetic bearing system

Abstract

In this study, a simple and smooth voltage controller for a three-pole active magnetic bearing (AMB) system is proposed. It is designed with the backstepping procedure. The first step assumes the currents as the control inputs and designs the smooth current controller that has been proposed in the literature. The second step considers that the currents are not actual inputs, but part of the states. Then, the actual control inputs (voltages) are designed using simple proportional and integral (PI) control to make the error states from the first step to be zero asymptotically. Based on the voltage-controlled AMB system, an observer is designed for the rotor displacement estimation. The observer is based on the input voltages and coil currents that drive the magnetic poles. Such an observer can be utilized in the sensorless control of the AMB system. Due to the strong nonlinearity in the dynamics of 3-pole AMB system, the theory of nonlinear high-gain observer is adopted to design the observer. First, it is shown that the strong nonlinear 3-pole AMB system is observable under the zero input condition, which guarantees the existence of a high-gain observer. Then, the system is transformed into a regular form for the design of observer. Finally, a nonlinear observer is designed following the theory of high-gain observer. The proposed smooth voltage controller and nonlinear observer are verified numerically and experimentally. The results show the effectiveness of the smooth voltage controller and the feasibility of the nonlinear high-gain observer.