Nonlinear H-infinity flight control of general six-degree-of-freedom motions

Application of nonlinear H-infinity control theory to Eight vehicles whose complete six-degree-of-freedom nonlinear equations of motion are considered directly without linearization is investigated, Nonlinear Right control mo des such as velocity control, body-rate control, attitude control, and hove ring control are designed in a unified frame-work such that the derived non linear H-infinity control law is valid for arbitrary flight vehicles. The m ost difficult and challenging task involved in applying the nonlinear H-inf inity control theory is to solve the associated Hamilton-Jacobi partial dif ferential inequality (HJPDI). We show that the HJPDI of Right control probl ems can be solved analytically with simple manipulations. A closed-form exp ression for the nonlinear H-infinity flight controller is derived from the solution of HJPDI and is shown to be in the simple structure of proportiona l feedback. The numerical simulations show that the derived nonlinear H-inf inity control law can ensure global and asymptotical stability of the close d-loop system and have strong robustness against wind gusts with varying st atistical characteristics.