  It is nontrivial to achieve global zero-error regulation for uncertain
nonlinear systems. The underlying problem becomes even more challenging if
mismatched uncertainties and unknown time-varying control gain are involved,
yet certain performance specifications are also pursued. In this work, we
present an adaptive control method, which, without the persistent excitation
(PE) condition, is able to ensure global zero-error regulation with guaranteed
output performance for parametric strict-feedback systems involving fast
time-varying parameters in the feedback path and input path. The development of
our control scheme benefits from generalized t-dependent and x-dependent
functions, a novel coordinate transformation and "congelation of variables"
method. Both theoretical analysis and numerical simulation verify the
effectiveness and benefits of the proposed method.
