Robust adaptive control of nonnecessarily inversely stable first-order systems

This paper presents an indirect adaptive control scheme for nominally controllable nonnecessarily inversely stable first-order continuous-time systems with unmodelled dynamics. The control objective is the adaptive stabilization of the closed-loop system with achievement of bounded tracking-error between the system output and the output signal given by a first-order stable reference model. A recursive least squares algorithm with normalization is used to estimate the plant parameters by using two additional design tools: 1) A modification of the parameter estimates and 2) a relative adaptation dead-zone.