Abstract
It is necessary for practical applications to design the adaptive control system which behaves robustly in the presence of unmodeled dynamics such as parasitics. As such robust schemes, the adaptive laws with σ-modification and with relative dead zone have been proposed. The latter scheme is attractive in the sense that the global stability can be guaranteed, but some problems such as how to specify the width of dead zone and the output error between the plant and the reference model arising from the use of dead zone are left to be resolved.
This paper presents a robust design method of the direct model reference adaptive control system in the presence of parasitics. In this method, the controller parameters are adjusted by an adaptive law with relative dead zone and the output error is reduced by a fixed feedback compensator. The stability of the overall system is analyzed using the singular perturbation theory and the Liapunov's direct method and then it is shown that the adaptive system is able to behave robustly to the sufficiently small parasitics if the width of dead zone is specified appropriately.
