Nonlinear PID predictive controller

A new class of nonlinear PID controllers is derived for nonlinear systems u sing a nonlinear generalised predictive control (NGPC) approach. First, the disturbance decoupling ability of the NGPC is discussed. For a nonlinear s ystem where the disturbance cannot be decoupled, a nonlinear observer is de signed to estimate the offset. By selecting the nonlinear gain function in the observer, it is shown that the closed-loop system under optimal general ised predictive control with the nonlinear observer is asymptotically stabl e. It is pointed out that this composite controller is equivalent to a nonl inear controller with integral action. As a special case, for a nonlinear s ystem with a low relative degree, the proposed nonlinear controller reduces to a nonlinear PI or PID predictive controller, which consists of a nonlin ear PI or PID controller and a prediction controller. The design method is illustrated by an example nonlinear mechanical system.