Roll autopilot design of a tactical missile using higher order sliding mode technique

Abstract

Tactical missiles are used against various aerial/ground targets which can be stationary or maneuvering. Tactical missiles should have highly efficient control scheme in order to intercept such targets with acceptable miss distance. It is known that aerodynamic characterization of the missile with high accuracy is very difficult. In addition to this, the inability to model the external disturbances make the autopilot design very difficult. Hence, the need for a robust control arises in the presence of parametric uncertainties and unmodelled external disturbances. Sliding Mode Control (SMC) which has got invariance property against external disturbances and the model inaccuracies has been applied to this plant. This paper concentrates on application of higher order sliding mode control for the roll autopilot design of a tactical missile. Conventionally, the roll autopilot is designed with roll angle and roll rate feedbacks. The addition of roll acceleration feedback helps to obtain a tighter control of roll dynamics especially during high angle of attack requirements. However, the roll acceleration is neither measurable nor estimable by numerical differentiation of roll rate feedback. A differentiator based on Super Twisting Algorithm (STA) is explored to estimate roll acceleration from roll rate measurement. The use of roll acceleration feedback in the autopilot ensures tight control of roll dynamics. The robust sliding mode control gains are designed using Linear Matrix Inequalities (LMI) based technique.