Robust Fractional Order Controller for sn Expendable Launch Vehicle

Abstract

Fractional calculus is an interdisciplinary area with multifarious applications especially in control systems due to more flexible parameters to adjust the dynamic behaviour of all the physical systems. This paper presents a fractional order controller structure for an expendable launch vehicle during ascent phase. The launch vehicle has highly flexible and unstable dynamic model, and in addition to that unpredictable control issues are caused by the sloshing of liquid propellants and the inertia problems of the engines. Under these circumstances controller with large robustness margins are required to meet deviations in model parameters which are unknown before the actual flight. The rigid body dynamics of the vehicle is considered for designing fractional order controller to overcome all these control issues. The robustness of fractional order controller is compared with existing classical controller for 20% variations in the aerodynamic coefficients. The stability margins of the open loop transfer function with all plant dynamics shows the supremacy of the proposed controller over the classical controller. The control inputs to launch vehicles, in the form of attitude commands, are affected by the wind. Hence the designed fractional controller simulated under the wind disturbance input and the result shows disturbance rejection capability of controller.