Optimized feedforward design scheme unifying regulator and command generator tracker

Abstract

Tracking control law is the control scheme to make the system output follow a nonzero reference command signal. By combining the tracking control law with an eigenstructure assignment and applying it to an advanced aircraft such as control configured vehicles, mode-decoupled command following can be achieved. The tracking control law usually consists of feedback control of output states and feedforward control of reference input. A new design methodology is proposed by utilizing the nonlinear optimization technique to design a useful controller. The proposed algorithm utilizes the eigenstructure assignment and the optimization technique to compute the feedback gain matrix (for aircraft mode decoupling) and feedforward gain matrix, respectively. It is shown that the existing algebraic formula for computing the feedforward gain matrix is the limiting case of the proposed methodology. The design methodology is illustrated by application to an AFTIF-16 aircraft. OR a multi-input/multi-output system, a given set of eigenvalues can be assigned by an infinity of gain matrices. The eigenstructure assignment technique utilizes this extra freedom to assign the closed-loop eigenvectors. The original eigenstructure assignment technique based on the algebraic solution is very useful for aircraft mode decoupling.13 The main drawback of this technique is the lack of stability robustness with respect to parameter variations. To solve this problem, research47 has been performed using optimization46 or the method of inequality. 7 In this paper, we are not very concerned with these feedback methodologies; thus, we just adopt the baseline eigenstructure assignment technique. Sobel and Shapiro2 developed the design methodology for pitch pointing flight control systems by utilizing an eigenstructur e assignment in conjunction with the command generator tracker.8 This methodology computes the feedback gain matrix by eigenstructur e assignment, then the feedforward gain matrix can be obtained by solving an algebraic unsymmetric Lyapunov equation. Therefore, this method does not allow the designer to use his own perspective for computing the feedforward gain matrix during the design process. In this paper, we propose a new design methodology for computing the feedforward gain matrix. The feedforward gains are computed to minimize a performance index, which considers both the error deviation from the prescribed model dynamics and steadystate error. By selecting the design parameters, the feedforward gain matrix will yield various tracking performances. We prove that the perfect model following control scheme is one of the limiting case of the proposed design methodology. The proposed design schemes are illustrated by application to an AFTI F-16 aircraft for pitch pointing control.