Switched control of a vertical / short take - o ff land aircraft : an application of linear quadratic bumpless transfer †

This paper describes the design of a switching scheme for integrated flight and propulsion control of a vertical/short takeoff land (V/STOL) aircraft throughout the hover and transition regions of its flight envelope. The approach adopted makes use of a recently introduced bumpless transfer technique and presents a methodology for switching between multiple controllers while limiting on-line computational overheads. The success of the switching scheme in maintaining desirable flying qualities as the aircraft accelerates from hover to wing-borne flight is demonstrated in non-linear simulation. Simulation results for the switched system clearly show the effectiveness of the bumpless transfer scheme in preserving closed-loop performance during switching. 1 INTRODUCTION frequencies and within the bandwidth of the closed-loop system. In this case, a single linear controller Over the past decade H2 and related branches that is designed to be robust to high-frequency of linear robust control theory have had consider-uncertainty may not be able to preserve adequate able success in the control of complex uncertain levels of stability and performance over the entire systems. Even in the case of high-order non-linear range of the system's operation. plants, linear robust control methods generally A commonly used tool to overcome this difficulty work with lower-order linearized models of the is the method of gain scheduling, whereby the para-system to be controlled. Uncertainty models are meters of a given linear controller are varied as a used to represent differences between the design function of the system's position in its operational model and the real system arising from many envelope. In other words, the linear controller actually sources, e.g. uncertain high-frequency dynamics, becomes a linear-based non-linear controller. This neglected non-linear actuator effects, etc. Typically, is particularly common in classical flight control these uncertainty models become significant at design where the gains of PID (proportional-integral-high-frequency ranges and therefore limit the closed-derivative) controllers and filters are scheduled as a loop bandwidth. However, non-linear systems such function of speed. Such schemes have been used as aircraft contain parameter uncertainties and successfully in the aerospace industry for years, non-linearities, which manifest themselves at lower although the subject of gain scheduling has been addressed rigourously from a theoretical point of view only comparatively recently [1, 2]. The develop