Simulation And Study On AC-AC Excitation System For AC Excited Generator

AC excited generator (ACEG) has superior performances such as good stability, variable speed constant frequency (VSCF) generation, active power and reactive power regulation independently and lag reactive power absorbing deeply. It is very suitable for hydroelectricity set, pump storage groups and wind power generation groups. It also makes good working to electric power system stability and supervlotage transmission system over voltage.Excitation control system plays an important role in utilize ACEG. So, the main purpose of this thesis is research and modeling excitation control system of ACEG.In this paper, the mathematical models of ACEG in static three-phase coordinate and in rotary two-phase coordinate are studied. The equations of ACEG in two-phase synchronous rotation coordinate are presented. The expressions of active power and reactive power of stator and rotor can be gotten in the d-q reference frame.This thesis adopts the vector control strategy of stator field oriented (SFO) and researches vector control of ACEG system. The vector control equations of ACEG excitation control system are gotten. The control strategy of ACEG VSCF generation and decoupling control of active power and reactive power is fixed.This thesis adopts AC-AC frequency converter by way of excitation source of ACEG. Through analyses of principle of AC-AC frequency converter's work, based on MATLAB/Simulink, the model of current-controlled AC-AC frequency converter is built, and based on S-function, the model of voltage-controlled AC-AC frequency converter is built.In this paper, based on MATLAB/Simulink, the complete simulation model of ACEG system is set up. It includes the model of ACEG, the model of hydro turbine and regulator, the model of AC-AC frequency converter, the model of vector control system and the model of excitation transformer. Based on this model, the decoupling control of active power and reactive power, the process of VSCF generation, the dynamic process like transition of supersynchronous and subsynchuronous speed of rotor, the limit of lag reactive power absorbing and the process of three-phase short-circuit at generator end are simulated. In the end, this paper analyses the FFT of the model. The result shows that using AC-AC frequency converter and stator field oriented vector control strategy can realize the independent rapid adjustment of active power and reactive power. During the process of adjustment, the frequency of stator voltage remains stably the same, and phase sequence of triphase rotor current changes when rotor speed is converted between supersynchronous speed and subsynchronous speed. The limit of lag reactive power absorbing of the model is in accordance with the result of theoretical analysis. AC-AC frequency converter is the most important harmonic source in ACEG system. The result of simulation is in accordance with the result of theoretical analysis. So the simulation model in this paper is correct.