In direct adaptive control, the adaptation mechanism attempts to
adjust a parameterized nonlinear controller to approximate an ideal
controller. In the indirect case, however, we approximate parts of the
plant dynamics that are used by a feedback controller to cancel the
system nonlinearities. In both cases, approximators such as linear
mappings, polynomials, fuzzy systems, or neural networks can
... [Show full abstract] be used as
either the parameterized nonlinear controller or identifier model. We
present an algorithm to tune the direction of descent for a
gradient-based approximator parameter update law used for a class of
nonlinear discrete-time systems in both direct and indirect cases. In
our proposed algorithm, the direction of descent is obtained by
minimizing the instantaneous control energy. We show that updating the
adaptation gain can be viewed as a special case of updating the
direction of descent. Finally, we illustrate the performance of the
proposed algorithm via a simple surge tank example