Adaptive Robust H_∞ Control For Power Systems

Electric power systems are multidimensional, nonlinear, complex, dynamic and large scale systems, which often contains various uncertain parameters and unknown disturbances. With the development of interconnection among powers systems, the complexity of the power systems also greatly increases. Thereby some dynamic problems which could threaten the operation of power systems in safe and stable mode are emerged. However, once power systems lose stability, the great loss and serious injury about national economy and peoples'life are resulted in if the faults are dealt with in improper ways. Therefore, it is becoming an important and urgent research topic to improve the operational stability of the power systems. Exploiting structure properties of electric systems combined with modern control techniques is an effective and promising approach.The dissertation proposes an adaptive backstepping robust H∞control aiming at nonlinear modeling for classes of power systems with uncertain parameters and unknown disturbances. The paper adopts an adaptive mechanism which does not follow the certainty equivalent principle combined with nonlinear H∞control, and then the robust stability of classes of power systems is researched. The main work is as follows:Firstly, the dissertation gives a brief introduction of stable significance, main objects and various control techniques of power systems at present. Then the adaptive mechanism which does not follow the certainty equivalent principle is briefly introduced.Secondly, a class of nonlinear system with lower-triangular structures is discussed. An adaptive backstepping robust H∞control method is proposed to the class of systems with uncertain parameters and unknown disturbances. The method adopts the above mentioned adaptive mechanism combined with nonlinear robust H∞control, and then the controller design is based on backstepping method. Because of combining adaptive control with robust control, the class of systems has adaptive tracking and learning ability, and also robust disturbance attenuation performance.Thirdly, the above mentioned research results are applied to an excitation control system, a main steam valve control system and a TCSC control system in FACTS for the first time, and the robust stability problems thereof are discussed in turn. Wherein, the adaptive robust H∞control method is applied to the excitation control system under the condition that the damping coefficient can't be measured accurately and the system is perturbed by unknown disturbances, and then the excitation controller is designed. Meanwhile, simulation result is presented and proves the effect of the design. Aiming at the main steam valve control system under the condition with uncertain parameters and unknown disturbances, the adaptive robust controller is designed, and the simulation result is presented also and proves the effect of the design. By applying the same methods, the corresponding controller is designed to TCSC system with uncertain damping coefficient and unknown disturbances.Concluding remarks are presented at the end of this dissertation. Some open problems are also pointed out, which deserve further study.