The sufficient richness and parameter convergence in MRAC systems: A direct approach using the theory of Liapunov

The sufficient richness condition plays an essential role in the convergence of parameter errors in Model Reference Adaptive Control (MRAC) systems. This condition has been derived based on the exponential stability property of linear time-varying systems. In this work, we outline a general and more direct approach that establishes the parameter error convergence; and hence exponential stability of the (nonlinear) system. A special view of this approach is describable by the well-known sufficient richness condition.