PERFORMANCE EVALUATION OF TWO NONLINEAR CONTROLLERS ON AN ATTITUDE SYSTEM USING SGCMG

This paper deals with the modeling and simulation of an attitude control system composed of three Single Gimbal Control Moment Gyroscopes (SGCMG) in a pyramidal configuration using two nonlinear controllers. The first controller is a first-order sliding mode which is robust to bounded uncertainties such as modeling simplifications, sensor noise and external disturbances, but it causes high frequency input, which can exceed the limit of the power systems. To overcome the drawback of the sliding mode, an I&I adaptive control is proposed. This controller estimates unknown parameters by introducing new states, resulting in smaller input gains and frequencies. At first, the dynamic model of SGCMG and the dynamic model of the attitude system were constructed. Based on this model, the steering laws of the SGCMG's for the two nonlinear controllers were designed. The simulation of the attitude control system is implemented in MATLAB. The simulation results show the effectiveness and the advantages of the proposed controllers.