Study On The Problems Of Adaptive Control For A Class Of Nonlinear Plants With Uncertain Hysteresis Input

Hysteresis is a property of a wide range of physical systems and devices, such as electro-magnetic fields, mechanical actuators, and electronic relay circuits. When nonlinear plants are preceded by the hysteresis input, the compound systems usually exhibit undesirable inaccuracies, oscillations or instability due to the nondifferentiable nonlinearities and severely limited characteristic of hysteresis. Nevertheless, most results of control theories are for linear or differentiable nonlinear systems, and they are not suitable for applying to nondifferentiable nonlinearities systems. Therefore, it is of great importance to develop new control approaches. The main research of the Master's thesis can be briefly described as follows:1. A backlash hysteresis loop is analyzed in detail. Firstly, it is expressed as a differential equation and its properties of nondifferentiable nonlinearities and severely limited characteristic are further studied. Secondly, from control point of view, the model of the hysteresis loop is developed and apply. Finally, the effect of parametric variation to hysteresis loop is studied through numeric simulations.2. Through analyzing the physical properties of the compound systems and combining them with adaptive control technique, a new robust adaptive control scheme is proposed to solve the tracking control problem of nonlinear compound system, where the hysteresis loop is input. The parameters of hysteresis loop are unknown but their bounds are known. The new scheme ensures the global stability of nonlinear systems with effective tracing to the given signal, and its validity has been verified through a simulations.3. By utilizing adaptive backstepping technique and a new fuzzy universal function approximator, a novel stable adaptive fuzzy backstepping control scheme is proposed. It deals with a class of unknown nonlinear dynamic plants preceded by uncertain backlash-like hysteresis input. Comparing with existing control approaches, neither the model of dynamic plants nor the bounds of uncertain hysteresis parameters are required to be known. The proposed control scheme can guarantee the stability of the closed-loop systems, and a simulation demonstrates the effectiveness of the proposed method.