Robust Controller Research For Small UAV

The modern UAV require high mobility, all-weather, all-inclusive line cruise flight in a complex environment, and the stability and flight performance requirements need to be ensured. Traditional control methods rely on accurate mathematical model; however, it is difficult to obtain a precise mathematical model in practice. Inevitable neglect of the higher order model dynamic during linearization, and the change of the model parameters caused by the transfer of the flight state, makes the design of flight control system difficult. Combining classic loop-shaping ideas with H∞theory, H∞loop-shaping design method based on left coprime factorization is proposed.Firstly six degrees of freedom UAV nonlinear model was established, and then selecting level, constant velocity, non sideslip flight as the reference flight condition, nonlinear equations were linearized according to small-disturbance theory. Neglecting the coupling between the longitudinal and lateral, the linearized equations obtained were divided into longitudinal and lateral state space equations.Singular value was introduced to instead of Bode plot which is usually used in the classical frequency domain design method. According to the sensitivity theory, the shape of the singular values curve which determines system performance was improved by choosing the appropriate pre-compensator and post-compensator. However the loop shaping of singular value curve cannot guarantee the stability the closed-loop system. Therefore, based on small-gain theorem, the H∞feedback controllers were designed to guarantee robust stability.UAV longitudinal and lateral flight control systems were designed using H∞ loop-shaping method. In order to verify the robustness of the system, the nonlinear simulation was implemented in Simulink, which show that the flight control system designed using the H∞loop-shaping method is robust under parameter uncertainty and constant wind interference.Studies have shown that the controllers design based on H∞loop-shaping method have good robustness. Especially for MIMO systems with right half plane poles, LQG/LTR and traditional H∞control method have limitations,while H∞loop-shaping design procedure has no the restrictions,is a feasible method.