Tham khảo tài liệu 'advances in flight control systems part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Adaptive Backstepping Flight Control for Modern Fighter Aircraft 47 Fig. 7. Manoeuvre 2 reconnaissance and surveillance performance at flight condition 1 with left aileron locked at 10 deg. 48 Advances in Flight Control Systems when online parameter update laws are used because these tend to be aggressive while seeking the desired tracking performance. Because the desired control signal is not achieved during saturation the tracking error will increase. Because this tracking error is not just the result from the parameter estimation error the update law may unlearn during these saturation periods. In Farrell et al. 2003 2005 a method is proposed that fits within the recursive adaptive backstepping design procedure and deals with the constraints on both the control variables and the intermediate states used as virtual additional advantage of the method is that it also eliminates the two other drawbacks of the adaptive backstepping method that is the time consuming analytic computation of virtual control signal derivatives and the restriction to nonlinear systems of a lower-triangular form. The proposed method extends the adaptive backstepping framework in two ways. 1. Command filters are used to eliminate the analytic computation of the time derivatives of the virtual controls. The command filters are designed as linear stable low-pass filters with unity gain from its input to its output. The inputs of these filters are the desired virtual control signals and the outputs are the actual virtual control signal and its time derivative. Using command filters to calculate the virtual control derivatives it is still possible to prove stability in the sense of Lyapunov in the absence of constraints on the control input and state variables. 2. A stable parameter estimation process is ensured even when constraints on the control variables and states are in effect. During these periods the tracking error may increase because the desired control signal cannot be .
