Design Of Optimal Excitation Controller Based On Power Grid Equivalent Methods

Excitation control system of synchronous generators can effectively improve the stability and dynamic quality of power grid. However, the performance of excitation control system can be affected by the change of external power grid structure and parameter, especially by the generator units in the same power plant or other units in the power plant nearby. Therefore, it is necessary to consider equivalent models of the external power grid while designing the excitation control system.This paper discusses research situation of excitation control methods and external power grid equivalent models in detail, and the mathematical model and basic theory are systematically introduced for the design of the optimal excitation control system. In order to consider static effect and dynamic effect of external power grid, parameter identification methods like the nonlinear least square method and the dynamic power flow fitting method are proposed for the static equivalent model and the dynamic equivalent model respectively. Simulation analysis based on Matlab shows that the equivalent models and parameter identification methods are reasonable and effective.After obtaining the parameters of the equivalent models, this paper establishes the linear mathematical model of the generator and power grid system, and deduces the state space equation for the linear optimal excitation controllers. The static linear optimal excitation controller(SLOEC) and dynamic linear equivalent optimal excitation controller(DLOEC) are designed respectively according to the optimal control theory.Finally, the two-machine infinite-bus system and the four-machine two-area system simulation models are built. Simulation analysis and comparative study on large and small disturbance indicate that compared to the conventional AVR+PSS control method, excitation control method the paper proposed can improve the power system's static stability and transient stability effectively, and also prove the effectiveness and superiority of optimal excitation controllers based on power grid equivalent models.