| With the rapid development of modern power systems,therefore they have some characteristics,such as large power grids must be connected together,distance transmission is very long and fast excitation devices must be used,etc.These characteristics are prerequisites for the development of modern power systems.Thus,the damping ability of excitation system can be reduced,leading the low frequency oscillation of power system is increased.Currently,the power system stabilizer PSS has shown that its effectiveness by reducing low frequency oscillations in power systems is the best.This is primary method has used by recommending Grid International Association.So,the PSS is usually used in power system stability,which has the potential to enhance damping ability of excitation system leading to reduce small signal,suppressing low-frequency oscillations and reducing disturbances.All problems above will do steady the power system.Therefore,countries on the world have used the power system stability to enhance damping ability of excitation system leading to reduce low frequency oscillations and improve the stability of power systems.However,the use of PSS for stable power system is not high effectiveness.To improve the performance,the parameters in PSS may be adjustment to adapt to each specific plant.Besides,in practical power system,the high nonlinear may be degrade the performance of the PSS.Thus,developed a new controller for power system stability is necessary.The main research contents of this thesis can be summarized as follows:(1)The thesis analyzes the phenomenon of low frequency oscillations in the power grid,indicating the faults of low frequency oscillations have occurred in countries in the world.This phenomenon has caused harm to the economy of the countries and as well as causing damage devices in power system.Thence,the importance of suppressing low frequency oscillations and reducing disturbance in power systems are necessary.(2)The thesis analyzes excitation system of electrical generator,which shows a significant impact to dynamic stability and static stability of power systems.Excitation system generates damping torque that the variations of it can reduce disturbance.Based on this characteristic,researchers have designed an auxiliary controller with the purpose provide control signal to enhance the damping torque for the excitation system.This damping torque may be suppressed low frequency oscillations as well as disturbances in power system.(3)The thesis analyzes the power system stability.And then,based on Krong-Hnang hydropower plant(in Vietnam)to set the parameters of the PSS2A,whose purpose is to increase the damping capacity of the excitation system to suppress the low-frequency oscillations on the power system.(4)The thesis studies a new controller to control complex systems.The PSS is used very effectively in linear systems,however,with nonlinear systems is not effective.Fuzzy control technique requires human knowledge and experience to set the IF-THEN rules.However,this defect can be overcome by combining among fuzzy and neural network.This hybrid controller is widely used in the field of automatic control with nonlinear plants.Hence,the study of the ANFIS controller for the problems of the power system stability has great significance.Consequently,we design ANFIS controller to replace PSS controller in Krong-Hnang hydropower plant(in Vietnam),which main purpose enhances damping ability of excitation system and suppressing low frequency oscillations in power system.(5)Finally,the use of MATLAB/Simulink software to simulate a single machine infinite bus system by establishing different faults and disturbances.Three systems operating mode simulation results of the non-PSS,the installation of PSS2A and the ANFIS controller are compared,analyzed and summarized.The results show that the performance of the ANFIS controller to suppress low frequency oscillation is much better than without PSS and PSS2A. |
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