It is well-known that sliding mode control is robust to matched uncert
ainties that lie in the range space of the input matrix. However many
systems are affected by mismatched uncertainties and yet do not enjoy
the matching conditions. It is the purpose of this paper to present a
new dynamical approach of sliding variable formulation which, when the
system is in sliding mode, can explicitly deal with mismatched uncert
ainties. Our first step is to treat certain states as inputs to a redu
ced-order system and use adaptive techniques to design fictitious cont
rollers for these inputs, which can then tackle the mismatched uncerta
inties. The second step is to use sliding control to realize the adapt
ive fictitious controllers. The design is systematic, modular and intu
itively simple.