Study On Improving Power System Daming By Using UPFC

Modern power systems, characterized by large capacity units, Extra High Voltage, long distance transmission, heavy load demand, are typical nonlinear, high dimensional, large-scale and dynamic systems. With the interconnections among different power systems, and the increasing numbers of newly introduced devices, a lot of issues on system security and stability raise up while the system size and complexity grow and make the generation and transmission more economic and efficient.More and more large-capacity generators with fast control excitation systems are put into operation. Along with the introduction of the competition mechanism by power marketing, the possibility of operating at the stability limit increases. Further more, since that transmission corridors are almost saturated; it is difficult to enhance transmission capability of power grid by building new transmission lines. The low frequency oscillation occurs more often in the large-scale interconnected system, which threatens the safety of system operation. Designing UPFC stabilizers for the purpose of damping power oscillation is an effective measure to improve system stability. The thesis presents systematic study on mathematic model of UPFC, optimization and Adaptive critic design of the UPFC stabilizer, et al. The main achievements are as follows:A small signal model of UPFC, which could be used in small signal analysis of power system, is established. Both calculation velocity and accuracy are considered during the model-establishing procedure. Furthermore, modular design enables it to communicate with other programs easily. The dynamic characteristic of capacitor voltage is taken into account. Besides, the bus voltage control, dc voltage control and power flow control, etc are included. With high precision, the model could be used in further study of the small signal stability in power system.Oscillation mode is analyzed by using system eigenvalues and the generator torque. The mathematical model including UPFC is derived based on modern control theory; meanwhile, the stabilizer is designed based on classic control theory. Design Procedure is controlled by the intrinsical link between modern control theory and classic control theory. In a multi-machine power system, the optimal location of stabilizers could be determined and the effective feedback signal could be obtained by the state-space equation. Further, the stabilizer could be implemented according to the results. The proposed method improves the damping level significantly and shown by simulation.A novel torque area method is proposed. For a modal frequency, the electrical damping and synchronizing torque coefficients are two main factors that influence the stability of power system, Damping and synchronizing torque components will be affected by the STATCOM stabilizer. By using torque area method, the design of STATCOM stabilizer is optimized and further more, it could maintains sufficient synchronizing torque as well as damping torque. In a 4-machine system, the stabilizer is also optimized; simulation shows the method is effective.Intelligent Soft Computing Methods is used to Design UPFC stabilizer to enhance stabilizer's adaptability. Typical linearized system models, namely model bank, are taken into account and corresponding linear stabilizers for various models are designed. Furthermore, the similarity between real system model and the model bank is evaluated by fuzzy logic, and the results obtained are used to adjust the weight of each linear stabilizer, and the whole procedure is adaptive according to system operating conditions. Therefore, the stabilizer works effectively and continuously. Finally, the simulation for a poor-damped power system is studied. Results shows that the proposed stabilizer improves the damping level significantly.