On the domain of validity of nonlinear H/sub /spl infin// control

The design of a nonlinear H/sub /spl infin// controller reduces to as the Hamilton-Jacobi-Isaacs (HJI) inequality. It proceeds by approximating the solution of the HJI equation. Intuitively, using a low order controller certain features of the closed-loop performance are sacrificed. In particular, we show that a nonlinear feedback control law will always result in a larger domain of validity than its linearized counterpart.