Application Of Synergetic Control Theory In Power System Stability Control

With the development of interconnection of the regional power grids and integration of bulk renewable energy power generation into power systems using long transmission lines, the structure of the power system becomes more and more complex; the operating condi-tions vary more and more frequently; the stability of the power system becomes more sig-nificant, thus the stability control of the power system has been attracted increasing atten-tions by the researchers and engineers. How to adopt a quick and accurate control measure to power system in the post-fault period to ensure its security and safety operation is an important issue of the development of the power industry.Synergetic control theory is a state space approach based on ideas of modern mathe-matics and synergetics. It uses nonlinear characteristics of the system itself, and can provide an effective means to design feedback controllers for a nonlinear system. A nonlinear sys-tem using synergetic control can hold the global stability on a manifold, and the synergetic controller is easily implemented in practice. In this thesis, based on the synergetic control theory in terms of improving the stability of the power system, the nonlinear power system stabilizer (PSS), the excitation nonlinear control of the synchronous generator, and steam valve nonlinear control of the turbogenerator has been studied, respectively. The whole the-sis consists of the following five parts:Chapter1summarizes the state-of-the-art development characteristics and the impor-tance of stability control of the power system, the current power system stability issues and its existing control methods are introduced, then the statuses in the field of the power sys-tem stability control are reviewed. Finally, the major research ideas and innovations of this thesis are clarified.Chapter2describes the theoretical basis and the design method of the synergetic con-trol, a linear system example is used to illustrate the design procedure and stability analysis of the synergetic controller. Moreover, four improved manifolds, which can be used to im-prove the performance of the synergetic control, are analyzed in detail.Chapter3proposes a synergetic control theory-based decentralized nonlinear power system stabilizer SPSS. A manifold.is established and the control law of the synergetic PSS is deduced based on the nonlinear model of synchronous generator using synergetic control theory. As all the input signals of the synergetic PSS are local measurements and inde- pendent of the parameters of the power transmission network, the decentralized control strategy can be achieved. Simulation results show that the proposed SPSS can effectively suppress power system oscillations and is robust with respect to the inaccuracies of the system model.Chapter4presents a synergetic control theory-based nonlinear excitation control method. A manifold is designed as a linear combination of the deviation of generator ter-minal voltage, rotor speed and active power for the synthesis of a synergetic excitation con-troller. Then the control law of the synergetic excitation controller is deduced. The influ-ences of controller parameters on control performance and its selection principle are also discussed. An adaption strategy is proposed for synergetic excitation controller to vary the control parameter in order to improve the performances of the voltage regulation and tran-sient stability under various operating conditions. Simulation results show the synergetic excitation controller can provide better damping and voltage regulation performances in comparison with the conventional power system stabilizer. Moreover, the controller em-ploys only local input measurements and a few controller parameters need to be determined, it is easy to be implemented in a practical power system.In Chapter5, based on synergetic control theory and feedback linearization technique, a novel steam-valve control method of the turbogenerator is proposed. A manifold is de-signed as a linear combination of the deviation of rotor angle, speed deviation and speed acceleration. Then, the precise linear model of a generator including the main regulator valve system is obtained. Based on this model, the control law of the proposed controller is deduced and the stability condition of the closed-loop system is analyzed subsequently. According to the requirement of primary frequency regulation, an additional PI controller is designed to dynamically track the steady-state value of the rotor angle. Case studies are undertaken based on a single-machine infinite-bus system and the New England system, respectively. The simulation results show that the proposed controller can suppress the power oscillations and improve transient stability more effectively in comparison with the conventional PID governor controller. Moreover, the proposed controller is robust to the variations of the operating conditions.