This paper presents a systematic methodology for the synthesis of global gain-scheduled controllers for nonlinear time-varying systems. A controller of this type is used to compute the pitch-axis autopilot of an air-air missile. The missile model used is considered a benchmark for testing autopilot controllers in the academic and industrial communities. The missile's dynamics are linearized at a small set of operating points for which proportional― integral/proportional-type controllers are designed, to shape the frequency response of the linear plants' dynamics. A new set of operating points is computed afterward using the connection between the gap metric and the H ∞ loop-shaping theory. Then, reduced-order, static, H ∞ loop-shaping controllers are designed for this set of points using linear matrix inequality optimization techniques. Finally, the global gain-scheduled controller is obtained by interpolating the proportional―integral/proportional and the loop-shaping controllers' gains over the missile's flight envelope. The simulation results given show the generality and effectiveness ofthe proposed control strategy in terms of the operating point selection, stability, performance and robustness, of the closed loop.

Missile autopilot design : gain scheduling and the gap-metric

Missile Autopilot Design: Gain-Scheduling and the Gap Metric

Over the last three decades, there has been increased interest in full authority (FA) control systems for helicopters. Despite their great potential, it will be some time before all operational helicopters are able to benefit from such flight control systems. Therefore, interim methods to deliver similar levels of performance are required, and it is natural to explore ways of improving current limited authority (LA) systems to achieve this. The study described herein investigates this topic and contributes a new LA design method.
The first part of the thesis describes the construction of the baseline FA controller for the AgustaWestland EH101 helicopter. The FA controller was designed using the 2DOFH∞ loop shaping methodology. Details of the controller design are presented, together with an analysis of linear and nonlinear simulation results. These reveal the controller’s abilities to provide good levels of performance, across the portion of the flight envelope tested, without the aid of gain scheduling.
The second half describes the derivation of state-space formulae that enables the transformation of the above (FA) controller into LA form such that the latter controller replicates the small-signal FA responses. Extensive analysis and simulations are carried out for this architecture, both at the design point and at other conditions throughout the flight envelope. Also, the results are contrasted against a simpler LA architecture and the effectiveness of the proposed LA controller over this is shown. Both FA and LA results are complemented by an evaluation of handling qualities information against the design standard ADS-33.
It is believed that the results presented in the thesis show the strengths of the proposed LA architecture and suggest that current helicopter hardware should be able to provide much of the functionality of FA systems without requiring a complete overhaul.

Systematic development of a limited authority flight control system for helicopters

This paper presents a systematic methodology in order to compute a nonlinear gain-scheduling controller for a missile autopilot. A nominal control is first calculated using an output-based equilibrium analysis of the system so as to properly track reference trajectories. A closed loop controller is then calculated as an interpolation of LTI static controllers to complement the nominal controller. These LTI controllers are computed on a small number of the plant's equilibrium points. The form of every local LTI controller is a cascaded one, namely an internal/external P/PI controller followed by an Hscrinfin loop-shaping static controller. The interpolation is performed according to the scheduling vector, which in this case is composed of the plant's output and Mach number. The results are motivated by the need for a predetermined-simple structure gain-scheduled control scheme, in order for it to be easily implemented and tractable on a real world application.

Static interpolated ℋ ∞ loop-shaping controllers for missile autopilot synthesis

This papers deals with the gain-scheduled control of the pitch channel of a missile with large variations of Mach and altitude. A reduced order $H_\infty$ loopshaping control technique allows designing discrete-time controllers of very small order for different flight points; the final control law consists in interpolating the parameters of the controllers so obtained.

Reduced order $H_\infty$ loop-shaping control of a missile pitch axis over a wide flight envelope

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Reduced order $H_\infty$ loop-shaping control of a missile pitch axis over a wide flight envelope