A Design Method for Robust Servo Controllers for Multi-Variable Nonlinear Systems Using an Approximate Linearization

In this paper, we propose a design method for robust servo controllers for nonlinear systems to which the exact linearization method is not applicable. In order for the output to follow the reference input without steady state error, the controller must include all modes of the reference input. Therefore we construct the augmented nonlinear systems with the plant and the pre-compensator that includes all modes of the reference input. Next, a state transformation matrix is settled, so that the augmented nonlinear system is transformed approximately into the controllable canonical form. A standard nonlinear linearization method is used to transform the controllable canonical form into a linear system. Since this method adopts an approximate linearization approach, in some cases, the approximate term makes the control system unstable. Next we present a design method for robust servo controllers that guarantee the stability of the control system even if the approximate term exists.