Nonlinear H∞ state feedback control for unstable plants

This paper gives a HJI inequality appropriate for nonlinear H_∞ state feedback control and gives a method to get nonlinear control law, the calculation process is clear and easy to understand. In linear system, unstable system is limited by Bode integral, and the optimal performance value is limited. Some literatures present that we can improve the performance during nonlinear area, and reduce the peak value of the sensitivity function. In this paper, we take maglev for example to design an nonlinear H_∞ state feedback system, the result illustrates that the performance can´t be improved by using nonlinear control law. This article also points out that for unstable plants, either with linear nor nonlinear control law, the system´s performance is objective limit.