Parametric robustness evaluation of a H-infinity missile autopilot

Abstract

A multivariable missile autopilot is synthesized using a H^ loop shaping procedure by McFarlane and Glover. Because missile flight control systems must guarantee stability and performance in the presence of large aerody- namic uncertainties, advanced p, tools are next used to analyze robust stability and performance of the control law in the presence of real parametric uncertainties in the stability derivatives. The multivariable H^ autopilot is proved to exhibit good parametric robustness properties. The control law is finally validated on a nonlinear simulator. New \JL tools are nevertheless also available: IJL sensitivities7 can bring further information in addition to the basic application of jit analysis, whereas the v tool811 can directly solve skewed ^ problems that would otherwise involve a recursive application of \JL analysis (e.g., robust performance problems or direct computation of the maximal s.s.v. over the frequency range). The use of these new JJL tools consequently enables further in- vestigation of the robustness properties of a controller beyond the basic application of the real/mixed \ji tool. We first illustrate on the //oo missile autopilot that the v measure can advantageously replace the s.s.v. in robust performance analysis. We then illustrate that the s.s.v., the v measure, and the JJL sensitivities can be combined so as to maximize in a rather systematical way the guaranteed domain of stability of the closed loop in the space of uncertainties. The paper is organized as follows. Section II describes the design objectives and the missile model. Section III is a general presen- tation of the //oo design with coprime factors and loop shaping. Section IV briefly reviews the /z tools used in this paper, whereas Sec. V describes the design of the autopilot and a first analysis of the control law. Section VI is devoted to the parametric robustness anal- ysis and to the validation of the autopilot on a nonlinear simulator. Concluding remarks end the paper.