Decentralized adaptive regulation with unknown high-frequency-gain signs

In this paper, we propose for the first time a decentralized adaptive contr ol scheme without requiring a priori information on subsystem high-frequenc y-gain signs. This is achieved by introducing Nussbaum-type functions in lo cal adaptive controllers, and developing a neu analysis approach which is q uite different from the conventional one used in centralized adaptive contr ol involving a Nussbaum-type function. With the help of integrator backstep ping, the decentralized control scheme can also be applied to high-relative -degree systems. The results of this paper enlarge the class of uncertain l arge-scale systems for which decentralized adaptive control can be designed .