Virtual outputs with uniformly asymptotically stable zero dynamics and feedback design
Conceptions of relative degree and minimum phase are connected to many control problems. To apply these conceptions to nonautonomous nonlinear systems one needs to know an output map which renders an nonautonomous affine system to be uniformly minimum phase. Necessary and sufficient conditions of the existence of such outputs are
presented in the multy-output case. Obtained conditions result in new setting of the stabilization problem and in a new set of time-varying stabilizing feedbacks. An example of a hovercraft trajectory stabilization is considered.