Robust adaptive algorithm with non-linear decay term

A new modified adaptive algorithm with a non-linear decay term is proposed to guarantee the robust global stability of continuous-time model reference adaptive control (MRAC) systems to unmodelled dynamics in the plant. The fundamental approach is due to Kosut and Friedlander (1985), but different robust stability results and adaptive features are shown because of the non-linear decay term. A sufficient condition to find the design parameters in the decay term which ensure the robust result is proved and its dependence on the tuned gains and unmodelled dynamics is discussed. The merits and demerits of our new algorithm are also discussed using a simple example for illustration.