Design Of Nonlinear Robust Adaptive Control For Power Systems Based On Backstepping Method

Power systems are strongly nonlinear, multidimensional, dynamic and large scale systems. With the rapid development of power industry, as well as the big leap in single unit capacity, the power network structure has witnessed a rapid increase in the size and complexity. Maintaining power system stability is thus one of the main concerns. The design of an advanced control system to enhance the power system stability margin so as to achieve higher transfer limits is one of the major problems in the study of power systems.In this dissertation, aiming at the nonlinear model of power systems and based on the backstepping methods, a series of stability control problems are studied, including excitation control, steam-valve control, and main FACTS devices control, etc. The main contributions are as follows.Chapter 1 firstly gives a brief review of power systems on the main control objects and the basic control problems. Then the stability of power systems and its new results are introduced, respectively. After that, the nonlinear control methods and their recent applications in power systems are introduced. Finally, the main work of this dissertation is sum up.In chapter 2, for a single machine-infinite bus system with thyristor controlled series compensation (TCSC) with internal parameter uncertainties and external disturbances, the robust H_∞control problem is addressed. Storage functions of control system are constructed based on adaptive backstepping and Lyapunov methods, then a robust H_∞controller and a parameter updating law are obtained simultaneously to ensure the transient stability of single-machine infinite-bus system with TCSC.In chapter 3, the robust control problem for FACTS is addressed via the proposed modified adaptive backstepping method. In the recursive design procedure of the feedback control law, the class-κfunctions are introduced to improve the transient response of the closed-loop system without exploiting a large controller gain in a long term.Based on chapter 3, chapter 4 combines the methods of both modified adaptive backstepping and sliding mode control in order to use the advantages of strong robustness of sliding mode control. The transient stability problem is studied for a single machine-infinite bus system with internal parameter uncertainties and external disturbances.Chapter 5 proposes a novel adaptive backstepping method which avoids the explosion of computation caused by repeated differentiation. At the same time, it is not necessary to construct Lyapunov function candidate for each subsystem at each backstepping step. Thus, the design procedure of the controller is much simplified. A nonlinear steam valve controller is designed by using the proposed method.Chapter 6 investigates the transient stability problems of a single machine infinite bus system with the generator excitation and TCSC, via coordinated passivation techniques. Two types of uncertainties, namely, the damping coefficient uncertainty and the modeling error of TCSC, are considered in the design procedure of the controller.In chapter 7, for the turbine speed governor system with input constraints, the transient stability problem is addressed. The problem of the control input constraints is solved via introducing the switching mechanism.Concluding remarks are presented at the end of this dissertation. Some interesting problems are also pointed out, which deserve further study.