Abstract: The design of a coarse pointing control system for optical communication terminals is a key factor that affects the process of setting up a communication channel. In this article, the disturbance moments arising from friction and eccentricity are analyzed for a periscope coarse pointing servo system. They are converted into a bounded unmodeled perturbation added to the brushless direct current (BLDC) motor. A terminal model using the state space method is deduced when model uncertainty and moment perturbation exist simultaneously. The linear matrix inequality (LMI) criterion is proposed when quadratic stability, disturbance attenuation and actuator input saturation problems are discussed through non-fragile state feedback. Finally, the BLDC model of communication terminals is investigated. According to the LMI criterion, the coarse controller is calculated by MATLAB toolbox. The simulation proves that the controller resists moment disturbance and saturation effectively, and possesses quadratic stability when bounded uncertainty of plant emerges.

Key words: optical communication, quadratic stabilization, disturbance moment, actuator saturation, linear matrix inequalities