This work addresses the attitude control of a satellite by applying MIMO quantitative feedback approach. The objective is to design a set of proper controllers in presence of unknown disturbances and parametric uncertainties for a nonlinear MIMO system. The physical model of satellite utilizes three reaction wheels as actuators. The controller goal is to change the rotational speed of reaction wheels to adjust the satellite in desired course. First, the mathematical model of satellite and its actuators using angular kinematics and kinetic equations is developed. Quantitative feedback theory is then applied to synthesize a set of linear controllers that deals with both nonlinearities in the equations and unknown parameters or disturbance sources. By using basically non-interacting desired outputs and extracting sets of linear time invariant equivalent (LTIE) plants, the controllers set is designed for nine SISO systems. Simulation of closed loop system shows that all desired specifications of closed loop (tracking, stability, disturbance rejection) are robustly satisfied.
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