Analysis Of The Impact Of Large Wind Power Integration On Power System Dynamic Stability

A key factor that affects the large grid interconnection is the dynamic stability, and the weak or negative damping of inter-area oscillation has earned much attention. With the rapid development of the technology and production, integration of wind power in the power system has become larger and larger in China. In recent years, more and more large-scale wind farms have been integrated into the grid, and the scale will be further enhanced. For the situation of power system integrated with large wind farm, the impact on the dynamic stability has not been studied adequately. This paper established mathematical model of different types of wind turbine for dynamic stability analysis. Dynamic characteristics of the wind turbines as well as the mechanism between the wind farm and the power system are illustrated. Finally, control strategy for the wind farm is proposed to provide additional damping for the inter-area oscillation.Firstly, the mathematical model for fixed speed, doubly fed and permanent magnet direct driven wind turbine is established for dynamic stability study. The mathematical model of the fixed-speed wind turbine includes:aerodynamic model, the squirrel-cage induction generator model, shaft model; the mathematical model of the doubly fed wind turbine includes:aerodynamic model, the equivalent generator and converter model, shaft model, the pitch angle control model, the converter control system model; the mathematical model of permanent magnet direct driven wind turbine includes:the equivalent generator and converter model, the converter control system model. Linearized status equations are derived according to the mathematical model established above. The equivalent model of a wind farm for simulation is described. And a novel method to calculate the equivalent wind speed is raised.Secondly, dynamic characteristics of different types of wind turbines are investigated through damping torque coefficient analysis. It demonstrates that FSIG and DFIG wind turbines are good for the damp of the power system, while PMSG is harmful for the damp of the power system.Thirdly, a two area test system is established to investigate the impact of wind power integration on power system dynamic stability. Eigenvalue calculation and modal analysis are used to evaluate the impact of wind power integration. Different factors are considered, including power system capacity, wind turbine types, wind farm locations and the variation of reserve capacity. The results demonstrate that the impact of wind power integration on power system dynamic stability is determinate by wind farm types, locations and the changes in power system operation due to wind power integration. Meanwhile, the connected system of Mengxi and North China grid is taken as an example to illustrate the impact of wind power integration. Eigenvalue analysis results demonstrate that the wind power integration in Wangquan grid has little effect on dynamic stability of the power system, while the wind power integration in Guyuan Grid can contribute to the damp of the power system. It is mainly determined by the location of the replaced synchronous generator during wind power integration.Finally, an additional damping controller in wind turbine is proposed to improve dynamic stability of the power system. When low frequency oscillation occurs in power system, the wide area signal is taken as input signal for the damping controller. The doubly-fed variable speed wind turbine regulates the electrical power output by controlling the converter, and injects damping active power to reduce the electrical power oscillation. A small test system created in the DSATool simulation software is used to verify the effectiveness of the proposed additional damping control. Simulation results demonstrate that the proposed additional damping controller in wind turbine can effectively improve the system damping, enhancing the dynamic stability of the power system. Also the effectiveness of the damping controller is verified through applying them to the wind farms in Guyuan.