Output Tracking of Nonlinear Nonminimum Phase Systems: an Engineering Solution

In this paper, we review some of design methods for output tracking of nonlinear nonminimum phase systems. Then we propose a control design procedure for output tracking of such systems which are stabilizable in the first approximation. The design procedure consists of two steps. In the first step the standard input output linearization is applied. In the second step, we group a subset of output with the internal dynamics as one subsystem, which is usually nonlinear, and the rest of output as the other subsystem which is linear; the nonlinear subsystem is linearized about its equilibrium; then we apply a two degree-of-freedom linear design procedure to each of two subsystems. The feedback part of the controller is designed to yield proper trade-off between disturbance rejection and robustness while the feedforward controller is designed to improve tracking performance.