On a new class of direct adaptive output feedback controllers for nonlinear square systems

Based on the recent development of sufficient conditions that allow nonstationary systems to become stable and strictly passive via static or dynamic output feedback, this paper presents a new class of direct adaptive output feedback controllers. The proposed control methodology uses a decentralized adaptation law mechanism based upon the Simple Adaptive Control technique. Using Lyapunov direct method and Lasalle´s invariance principle for nonautonomous systems, the formal proof of stability is established. The applicability of the proposed adaptive control approach to second-order Euler-Lagrange systems, whose nonlinear dynamics is expressed in the operational space, is presented.