Adaptive fuzzy control for nonlinear systems without strict-feedback form

For the first time, this paper addresses the problem of adaptive fuzzy control for nonlinear non-strict-feedback systems with input saturation. To deal with the non-smooth input saturation nonlinearity, a smooth function in non-affine structure subject to the control input signal is used to approximate the input saturation function with a bounded approximation error. Based on the monotonously increasing property of the system bounding functions, a variable separation method is developed to overcome the difficulty from the non-strict-feedback structure for control design. A novel adaptive fuzzy control scheme is developed without the prior knowledge of the bound of input saturation. It is shown that the proposed controller guarantees that all the signals in the closed-loop systems are semi-global bounded. A numerical example is used to illustrate the effectiveness of the proposed approach.