Networked Control Of Power Systerm Stabilizers Considering Random Delay

The low frequency oscillation problem has become increasingly prominent, bringing much harm to the safety and stability of the operation of power grid. It is proved that the use of power system stabilizer (PSS) to suppress low frequency oscillation is an economic, efficient, simple and also the most widely used method. It has gained more consideration of the power system research. Since the conventional feedback signal of the PSS is restrained by feedback signal, it cannot effectively suppress inter-area oscillation of interconnected power system. WAMS based on Phasor Measurement Unit (PMU) can measure information related to the low frequency oscillation in different parts of the plant (substation), and transfer the information to the other related units in the system with the help of communication technology. With the application of WAMS, the introduction of wide-area signals as the feedback control signals of PSS breaks the limitation of the conventional PSS and has a broad development prospect. In the process of the collection and transmission of the information, delay is unavoidable. Thus the research on delay problem in the wide-area measurement system has received extensive attention in the power industry.Faced with the problem of random delay, this thesis puts forward a wide-area PSS design scheme considering random delay, and establishes the simulation model of two-area power system. The results of the simulation show that the presented control method is effective and feasible.Main work of this thesis is as follows:1) Starting from the mechanism of low frequency oscillation, the suppression measures of low frequency oscillation are discussed, the analysis methods of low frequency oscillation are introduced, and the characteristics of the system are analyzed through the eigenvalue method.2) Models of single-machine infinite-bus system are analyzed, and the mechanism of the low frequency oscillation is also analyzed based on the influence of excitation regulation system. The linearized models of single-and multi-machine systems used in the small disturbance analysis are also described.3) The structure of the wide-area measurement system is introduced. The phase characteristics of wide-area signals are analyzed. The causes and components of delay in the wide-area measurement system are introduced as well. Besides, with the help of Bode diagram, the influence of delay on the wide-area measurement system is analyzed. The system delay effect processing is discussed.4) Faced with random delays, this paper realizes a compensation scheme by using a compensator which can analyze the size of delay online and compensates the delay sector by sector. To testify the effectiveness of the scheme, simulation tests are accomplished using a two-area power system.