Robust Fuzzy Tracking Control For Continuous Nonlinear Systems And Its Application In Medium Speed Pulverizers Of Power Plants

The tracking control problem of nonlinear systems has been extensively investigated by a number of researchers and many results have been made over the past decade. By far, most tracking controllers of nonlinear systems can't track the desired trajectory asymptotically. They also can't consider such performance indexes as robustness, H₂ performance, H_∞performance at the same time, cew tracking control schemes can make the output of a nonlinear system track the desired trajectory asymptotically by adopting the adaptive scheme, e owever, these schemes will make control systems slower. Aiming at the above problem, this paper will propose several fuzzy tracking control schemes which can consider important performance indexes of tracking control systems with guarantee of their real-time characteristic. These control schemes can make the output variables of continuous nonlinear systems (nonlinear systems for short) with uncertainties track the desired trajectories asymptotically. At the same time, the control schemes can attenuate the effect of external disturbance and maintain internal stability of the close-loop systems, curthermore, the tracking control system of a pulverizer of a power plant is designed according to the proposed fuzzy tracking control scheme. Control performance of the new tracking control system is better than the former control performance. The main work is generalized as follows:1. The fuzzy asymptotically tracking control scheme for nonlinear systems is presented. The internal model of the desired trajectory and the external disturbance is embedded in the control system to counteract the unstable poles of the disturbance and trajectory. Thus the output variable of the nonlinear system can track the desired trajectory asymptotically and the external disturbance can be attenuated without adaptive control scheme. The corresponding fuzzy observer is presented to deal with the condition that the state variables are not measurable directly. The sufficient conditions of stability of the fuzzy tracking controller, its corresponding observers and the fuzzy tracking system containing a controller and a observers are proven to guarantee the validity of the presented control schemes. Then the simplified design methods of fuzzy tracking control are introduced.2. The robust fuzzy tracking control scheme is proposed which can satisfy the H_∞disturbance attenuation performance. Compared to the fuzzy asymptotically tracking control scheme, the proposed scheme considers the approximation error in the T-S fuzzy model and the H_∞disturbance attenuation performance. It can make the output variables of nonlinear systems with external unknown disturbance track the desired trajectories very well. The corresponding H_∞fuzzy observer is also presented to deal with the condition that the state variables are not measurable directly. Furthermore, the sufficient conditions of H_∞fuzzy tracking controller, its corresponding observer and the H_∞fuzzy tracking control system are proven.3. The mixed H₂/H_∞robust fuzzy tracking control scheme is proposed. The approximation error between the output of nonlinear system and its corresponding T-S fuzzy model is considered. So the T-S fuzzy model is closer to the nonlinear system. The mixed H₂/H_∞robust fuzzy tracking control scheme can make the output variable track the desired trajectory very well while the H_∞disturbance attenuation performance and H₂ optimization performance are satisfied at the same time. The stability of the mixed H₂/H_∞, robust fuzzy tracking controller and control system containing a controller and a observer are proven to ensure the validity of proposed control scheme.4. The robust fuzzy asymptotically tracking control scheme of nonlinear systems is proposed. The uncertainties in nonlinear systems are expressed as the parametric uncertainties in T-S fuzzy model. Internal models of the desired trajectory and the external disturbance are embedded in the robust fuzzy tracking control system so that the control system can track the desired trajectory asymptotically and the effect of disturbance can be attenuated effectively. The disturbance attenuation performance is improved. Then the sufficient conditions of stability of robust fuzzy tracking controller, its corresponding observer and the robust fuzzy tracking control system are proven.5. Based on the analysis of operation mechanism of a medium speed pulverizer, its present nonlinear mathematical model is improved. Then a T-S fuzzy model of a medium speed pulverizer is proposed based on the improved model, enabling easy design of the control system for the pulverizer. The T-S model is composed of several linear models which can be obtained by identifying a group of constant coefficients with the aid of genetic algorithms. It is equivalent to the improved model of a pulverizer. The actual modeling results show a satisfactory agreement between the T-S fuzzy model response and the measured data, confirming the effectiveness of the proposed model.6. The design process of control system of a medium-speed pulverizer in the DCS hardware platform is introduced. The design procedure of fuzzy asymptotically control system is summarized. Then the robust fuzzy control system design software of a pulverizer is developed which makes it easy to develop the tracking control system and perform the simulation examination for an engineer. Simulation examples of a pulverizer under desired trajectories of a step signal and a complex signal are given to illustrate tracking performance of the proposed tracking control system.