Two-DoFs active deflection control of MSW based on fractional-order integral SMC method

Abstract

The active deflection of the rotor shaft in the magnetically suspended wheel (MSW) could generate three-dimensional torques to realize the attitude control of spacecraft, but the torsional torque and nonlinear torque could affect the control precision of active deflection. Therefore, a fractional-order integral sliding mode control (SMC) method is designed to improve the control precision and robustness of active deflection. Firstly, the electromagnetic (EM) torques generated by the three degrees of freedom (DoFs) axial magnetic bearing (MB) are analyzed, and the torsional torques of two-DoFs MB are developed during the active deflection process of the flywheel rotor. Results show that the active deflection is affected by the nonlinear EM torques and torsional torques. Furthermore, the fractional-order integral SMC law is designed to improve the control performance of active deflection, and the closed-loop stability of active deflection with the fractional-order integral SMC method. Finally, the simulations and experiments are conducted to verify the control performances of the proposed method, and experiment results indicate that the angle obviation of active deflection is reduced by 50% compared to the general PID control with the cross-feedback model.