Improved prescribed performance control of a fast steering mirror based on switching strategy

To meet the high-performance control requirements of a fast steering mirror in a laser communication system, an improved prescribed performance control method that combines a reduced-order nonlinear extended state observer and a fast nonsingular terminal sliding mode is proposed. First, a reduced-order nonlinear extended state observer is constructed to estimate the external disturbance of the system. The estimated value is then introduced into the controller for feedforward compensation. Subsequently, a prescribed performance control law is designed based on the prescribed performance function to achieve constrained control of the system's tracking error. Second, to address the fragility issue of prescribed performance control, a switching fast nonsingular terminal sliding mode control law is established to avoid control singularity. The finite-time stability of the closed-loop system is then proved based on Lyapunov stability theory. Finally, the effectiveness and superiority of the proposed control method are verified by comparative experiments. This proposed method especially serves as a good guide for controller designs of other precision optical instruments.