A robust adaptive controller with minimal modifications for discrete time-varying systems

The goal of this paper is to show that an indirect adaptive controller with parameter projection as the only modification on the basis of conventional adaptive control algorithms can globally stabilize systems having fast parasitics, bounded external disturbances, and time-varying parameters without any restriction on signals in the closed-loop system such as persistence of excitation. Further, the controller can still retain the properties of earlier unmodified conventional adaptive controllers when the controlled plant satisfies so-called “ideal assumptions” or the rates at which the plant parameters change belong to the l₁ (or l₂) space