特征结构配置在飞行控制系统设计中的应用

Improvement in Application of Eigenstructure Assignment to Flight Control System Design

本文研究了输出反馈的特征结构配置方法在飞行控制系统设计中的应用,对于n阶m个输入、r个输出的线性可控、可观测系统,该方法可精确配置max(m,r)个特征值,而其余未配置的开环特征值会发生变化,对系统稳定性有一定影响。为了便于工程实现,讨论了有约束的输出反馈特征结构配置,推导了模型跟踪的前馈增益算式。最后举例说明了该方法在直接力控制律设计中的应用。

There are two ways to realize eigenstructure assignment. One way is the use of full state feedback, which can assign all eigenvalues / eigenvectors, but requires reconstruction of state and makes its practical implementation relatively difficult[4].Another way is the use of output feedback, which is usually employed to design flight control system[1-8]. To the authors' best knowledge, there is no published paper on the stability properties of eigenstructure using output feedback. This paper presents results of our research on such stability properties. For a controllable and observable linear system with n states, m inputs and r outputs, the method of output feedback assigns r eigenvalues that satisfy the design specification, but the remaining (n-r) the eigenvalues may or may not satisfy design specification. If some of the (n-r) eigenvalues do not satisfy the design specification, then instability occurs. This is the shortcoming of the usual method of output feedback. The authors' opinion is that when such a situation occurs, the r eigenvalues / eigenvectors should be reassigned as often as necessary until all n eigenvalues satisfy design specification.Usually two or three reassignments suffice. The authors' research shows that the introduction of easily implemented constrained output feedback can make controller structure simple and increase its operational reliability. After due consideration of the control characteristics of the flight control system, we can impose constraints on the feedback matrix in the form of assigning zeroes to some elements in the matrix, i,e. certain unimportant outputs are not fed to certain inputs. It gives the designer the opportunity to examine a spectrum of tradeoffs between performance and complexity / reliability. In the design of a specific flight control system, both output feedback and contrained output feedback are used and the results are presented in Table 2(control law) and Figs.2 and 3(simulation results). Table 2 and Figs. 2 and 3 show that the introduction of constrained output feedback does make controller's structure simple and increase its operational raliability.