Modification of a steepest descent control for output tracking of some class non-minimum phase nonlinear systems

The problem of output tracking for a class of nonlinear systems whose zero dynamics are not necessarily stable is addressed in this paper. To solve the problem, we transform the systems into a normal form which is minimum phase with respect to a virtual output, which is a linear combination of state variables. By applying the modified steepest descent control, the system output track to the desired output.