Changing the unstable zero dynamics of nonlinear systems via parallel compensation

This paper deals with the unstable zero dynamics of nonlinear systems. It is well understood, that for many control schemes like adaptive control, model matching, exact linearisation and much more there exist a necessary assumption: the controlled system has to be minimum phase, i.e. the zero dynamics must be stable. This paper shows that for analytic systems with linear inputs (ALS) a linear parallel compensator is sufficient to change the unstable zero dynamic of a given ALS to a stable zero dynamic. A control scheme suitable for minimum phase systems only then can be used for the substitute system consisting of the given ALS and the parallel compensator.