Robust stabilization of MIMO nonlinear systems by backstepping

The problem of global robust stabilization is investigated for a class of multi-input, minimum-phase nonlinear systems with unknown time-varying parameters or disturbances belonging to a given compact set. It is assumed that the systems admit a special structure, which is much more general than strict feedback form. It is shown that such a structure makes it possible to construct both Lyapunov functions and robust stabilizing controllers by the backstepping method.