In this paper a modified model reference adaptive control (MRAC) technique is presented which can be
used to control systems with nonsmooth characteristics. Using unmodified MRAC on (noisy) nonsmooth
systems leads to destabilization of the controller. A localized analysis is presented which shows that the
mechanism behind this behavior is the presence of a time invariant zero eigenvalue in the system. The
modified algorithm is designed to eliminate this zero eigenvalue, making all the system eigenvalues stable.
Both the modified and unmodified strategies are applied to an experimental system with a nonsmooth
deadzone characteristic. As expected the unmodified algorithm cannot control the system, whereas the
modified algorithm gives stable robust control, which has significantly improved performance over linear
fixed gain control
