Nonlinear H/sub ∞/ missile longitudinal autopilot design with θ-D method

Abstract

In this paper, a new nonlinear control synthesis technique, the /spl theta/- D method, is employed to design a missile longitudinal autopilot. The /spl theta/-D technique yields suboptimal solutions to nonlinear optimal control problems in the sense that it provides approximate solution to the Hamilton-Jacobi-Bellman (HJB) equation. Semi-global asymptotic stability can be achieved by manipulating the perturbation terms which are added to the cost function in developing a series solution. Furthermore, this method can be used to provide an approximate closed-form solution to the state dependent Riccati equation. The particular /spl theta/-D methodology adopted in this paper is referred to as /spl theta/-D H/sub /spl infin// design. The /spl theta/-D H/sub /spl infin// design has the same structure as that of linear H/sub /spl infin//, except that the two Riccati equations are state dependent. By using the /spl theta/-D technique, we would eliminate the need for online computations of Riccati equations as in the recently popular state dependent Riccati equation technique. A missile longitudinal autopilot design demonstrates the capabilities of /spl theta/-D method.