Robust adaptive control: from theory to practical applications to aerospace systems

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The overall goal of the proposed research program is to develop a novel methodology for the design of robust scheduled flight control systems with adaptation capabilities, as well as the attending validation procedures. The development, integration and clearance of electrical flight control systems (EFCS) are tedious, costly and time­-consuming processes. In addition to standard requirements related to stability, accuracy and transient behaviour, the EFCS must meet stringent specifications composed of flying and handling qualities that reflect the ease to fly the plane. Moreover the EFCS have to be robust to external disturbances (e.g. wind, gust), varying parameters (e.g. mass, inertia, centre of gravity location), and to underlying mathematical model uncertainties and partial failures. The dynamic behaviour of an aircraft varies greatly within its flight domain and one single linear time­-invariant controller cannot ensure robust performances over the whole flight envelope. For several decades, engineers have resorted to gain­-scheduling techniques to design flight controllers. Traditionally, gain-scheduling consists in designing linear controllers over a gridding of the flight envelope; controller gains are thus updated according to scheduling variables that are representative of the flight condition (e.g. altitude, Mach number, airspeed). The controller gains are stored in look-­up tables and multilinear interpolation is used to compute the gains at every operating point. This approach provides working solutions but is a cumbersome iterative process that involves many trials and errors loops. Moreover, the designed controllers are seldom optimal or robust. The main objective of this research program is to develop solid practical tools based on novel theoretical approaches that will facilitate and improve controller design for aerospace systems. We will focus on the three following major challenges: 1. The first challenge lies in the synthesis of fixed-structured controllers that can be easily scheduled to cover the entire operating domain, as well as control methods that can solve this problem as a whole. To this end, our first objective is to capitalize on hitherto unexploited powerful theoretical results in robust control such as the guardian maps to develop procedures that yield robust scheduled controllers with respect to the operating domain. 2. The second challenge concerns the global stability assessment of the scheduled controller. Indeed, as the controller synthesis is usually performed on a finite number of operating points, the stability at every other point is not guaranteed. Therefore, the second objective proposes to develop and to use novel tools based upon guardian maps to assess performances and robustness over the whole operating domain. 3. Finally, the third challenge consists in recovering performance versus encountered uncertainties or system failures. The renewed interest in adaptive methods for aerospace systems provides new tools that can be advantageously used to enhance baseline controllers. To this end, the third objective aims at augmenting the robust baseline scheduled controller with an adaptive loop. These newly developed methods and subsequently tools will greatly benefit the aerospace industry by reducing development costs and saving development time of flight control systems.