The design of nonlinear PID and PI attitude-controller for a flexible spacecraft
挠性航天器的非线性PID和PI姿态控制器设计

A model-independent nonlinear PID attitude-controller is proposed for a flexible spacecraft with model uncertainties and constant disturbances. This controller approximates to a classical linear PID controller when the attitude error is small. In addition, a nonlinear PI controller which only requires attitude measurement is also designed for the case of gyros failure. Both of the proposed controllers exhibit the disturbances rejection properties in a local region, and render the attitude control system semi-globally stable in the case of no disturbance. To solve the stability analysis problem arising from the integral term, we employ the singular perturbation theory to analyze the stability of the resulting closed-loop system. Finally, numerical simulations are included to demonstrate the performance of the presented controllers.