Command filtered back-stepping missile integrated guidance and autopilot based on extended state observer

Introduction

Since 1980s, there have been lots of studies in the area of missile integrated guidance and control (IGC). In the conventional design, the missile guidance and control system is treated as two separated processes based on different operation frequencies. The outer guidance system creates acceleration or angle of attack (AOA) command, and the inner control system tracks it. When the two control loops are combined, the original performance objectives are lost and must be recovered. Thus, the resulting iterative design may not produce an optimal overall system. Additionally, under the condition of high speed, imprecisely known aerodynamics, complicated uncertainties, and external disturbances, the missile dynamics is obviously characterized by nonlinearities. The approaches which involve linearization about a set of equilibrium conditions or trim points within the flight envelop suffer from several disadvantages. Comparatively, the IGC design has provided better solutions in low-cost, modular growth, design flexibility, simple logistics and attracted great interest of researchers.

In Williams et al.,¹ the scheme of tactical missile IGC system is designed, where the information produced by inertial sensors of guidance system are used for the attitude control system. Because the accuracy of sensors in guidance system is much greater than that of autopilot, the IGC can reduce cost and improve the entire guidance and control system performance. In Evers and Cloutier,² the discussion of IGC scheme goes a step further with three optimal control laws for a tactical missile. In Xin et al.³ and Vaddi and Menon,⁴ new optimal control methods are proposed to effectively design IGC system for missiles. However, the weighting matrices have too many elements, while the actuator dynamics is assumed to be sufficiently fast and is not modeled in the IGC development. In comparison, sliding mode control (SMC) is a robust method with not complicated structure for nonlinear control issues. It has been extensively used in IGC design. In Shima et al.,⁵ a brief review of SMC is made at first. A simple first-order actuator dynamics is considered in model development. Then, the missile IGC design is compared with two different separated designs. It is indicated that the inherent instability of decoupled guidance and control loops in terminal phase is postponed by the integrated design, so the interception...