Simultaneous state and dead-zone parameter estimation using high-gain observers

In this paper we propose a new methodology of estimation of nonlinear systems subject to unknown hard-input nonlinearities. Using the fact that the dead-zone input nonlinearity can be modelled as a line input function with a bounded disturbance term then, by appropriate selection of the system input, we show that the simultaneous estimation of the dead-zone parameters with the unmeasured system states is possible under some mild conditions. The proposed observation strategy can be applied to both symmetric and non-symmetric dead-zone input with possible extension to time-varying dead-zone characteristics. Several cases are considered with illustrative examples in order to show the effectiveness of high-gain observers in identification of the dead-zone parameters.