Research On Fuzzy Control And Networked Control For Nonlinear Systems

Since the fuzzy control theory was proposed, it has been regarded as an effective way to deal with the problem of analysis and control for complex nonlinear systems. It is important in fuzzy control field that research on stability analysis and con-troller design via different fuzzy models. Also, in recent years, the improvement and generalization of existing results has been a hot topic. In addition, the tendency of industrial systems is becoming interconnected via a communication network. How-ever, despite the advantages and potentials, communication network in the control loops arouse some new issues, which imposes a challenge to system analysis and de-sign. In this dissertation, various control problems are investigated for some classes of nonlinear systems based on fuzzy hyperbolic model (FHM). Moreover, the robust control problem is addressed for nonlinear networked control systems (NCS) based on T-S fuzzy model and FHM respectively, which provides new results and new ideas in the fields of nonlinear system control and networked control. The results are given based on Lyapunov theory and linear matrix inequality (LMI) technique. The main contents of the dissertation can be briefly described as follows:1. Based on FHM, the analysis and control problem is studied for a class of continuous-time nonlinear systems. First, considering the influence of both approxi-mation error and external disturbance, a fuzzy hyperbolic H∞controller is presented. The proposed methods are then easily extended to a system with polytopic-type uncertainties. Next, an integral sliding mode controller design method is presented based on FHM. The synthesized sliding mode controller guarantees the reachability of the specified sliding surface in finite time interval.2. Based on fuzzy hyperbolic model with time delays (DFHM), the stabil-ity analysis and controller design is concerned for a class of nonlinear systems with time delays. First, the nonlinear system with time delays is represented by a DFHM. Then, a novel Lyapunov-Krasovskii functional is used, and the sufficient conditions for asymptotic stability are derived. The proposed methods have been extended eas-ily to a system with either polytopic-type or norm-bounded uncertainties. Next, by using delay-independent Lyapunov functional approach, some sufficient conditions for the existence of a mixed H2/H∞controller are provided.3. Based on FHM, the analysis and control problem is studied for a class of discrete-time nonlinear systems. Applying FHM's characteristics, the design of reliable controller, mixed H2/H∞controller, and non-fragile controller is discussed respectively. During the design process, the Lyapunov matrix P can be relaxed from a diagonal positive matrix to a diagonally dominant positive matrix, which can lead to less conservative results.4. Based on T-S fuzzy model, the robust H∞controller is designed for non-linear networked control systems with uncertainties. Both network-induced delay and packet dropout are addressed in a unified framework. The proposed controller can guarantee asymptotic stability of the closed-loop system and satisfy H∞per-formance. Also, in the proposed approach, the maximum allowable control intervalδis adopted to reflect both the network-induced delay and packet dropout prob-lems. Moreover, the network-induced delay doesn't need to be restricted within one sampling period.5. The robust control problem is considered for a class of nonlinear networked control systems via model-based approach. First, the controlled plant, which is nonlinear and with external disturbance, is represented by a T-S fuzzy model. Next, the fuzzy estimator (FE) is used to estimate the states of the controlled plant for the purpose of effectively reducing the network burden. The control input signal is established by the states of FE. Sufficient condition for the robust stability of the closed-loop system with H∞performance is obtained.6. Based on FHM, the networked control problem is studied for a class of continuous-time nonlinear systems. The controller design method is presented based on a delay-dependent approach and the sufficient conditions for asymptotic stability of the closed-loop system are obtained, by exploiting a new Lyapunov-Krasovskii functional and by making use of novel techniques for time-delay systems.Finally, concluding remarks are given. Some unsolved problems and develop-ment direction for fuzzy control and nonlinear NCS are proposed. Further, the prospects of the future study are given.