Regulation and large motion tracking for active magnetic bearing system using sliding mode control

Abstract

In this thesis, sliding mode control (SMC), one of nonlinear control theories is designed based on the original nonlinear active magnetic bearing (AMB) system with 4 degrees of freedom. It is applied to the regulation/stabilization and large motion tracking of the nonlinear rotor AMB system. For the regulation of rotor, the vertical rotor AMB system with the imbalance disturbance due to the eccentricity of mass is considered for cylindrical and conical mode initial conditions. For the large motion tracking, the horizontal rotor AMB system with uncertain parameters, e.g., the force constant, nominal air gap from AMB actuator, the cut-off frequency of power amplifier, is considered. The large motion tracking is composed of two parts: radial motion tracking (RMT) and axial motion tracking (AMT). For RMT, the whirling and conical motions are used as desired tracking trajectories. For AMT, Albemet and Steel are used as the material of rotor. MATLAB/SIMULINK software is used to simulate both the AMB systems with SMC's. From the simulation results, it is shown that (1) for the vertical rotor, SMC designed based on nonlinear AMB system can attenuate uncertain imbalance disturbance for both cylindrical and conical mode initial conditions, (2) for RMT of the horizontal rotor, the AMB system for conical desired motion is more robust to parametric uncertainty and energy-efficient, and (3) for AMT of the horizontal rotor, according to the maximum shooting target and the total heat loss generating from the axial bearings, Albemet rotor, which has low weight and high stiffness is recommended. It is also verified that bias current of AMB actuator is important factor to reduce the total heat loss.