A Study On Small Signal Stability Of Large-scale Wind Power Integration

With the increase of development efforts of wind sources, wind power has got much attention as a new type of clean energy. The transmission grid in China strides across a long distance and has a heavy load which leads to the security problems of small signal stability existed. With the integration of large scale wind farms to the grid, the complexity of the problems would definitely be increased. As a result, the study of small signal stability of large-scale wind power system connected to the grid has important theoretical and practical significance.This paper analyzes the relationship both between regional and wind speed, and between the number of generators and wind speed. Thus, this paper establishes a model of a complex wave to descript the equivalent wind speed of the wind farm with the number of generators considered as a variable element. Then based on the modular decomposition of doubly-fed induction generator(DFIG), we equivalence the wind farm to a single generator.According to the eigenvalue analysis method, this paper analyses the physical significance of the damping ratio and other parameters. Then this paper points out when the oscillation frequency is low, damping ratio cannot completely describe the characteristics of the oscillation of the system. This paper discusses the meaning of each oscillation mode with DIgSILENT/Power Factory, and analyses the inter area oscillation mode in detail, which exist the largest security risk, and then prove the problems of the existing analysis method.Finally, this paper puts forward the definition of the parameter of the damped oscillation and uses it as the main criterion to analyses the oscillation mode which is strongly related to the equivalent wind farm. The simulation shows that the equivalent wind farm would bring in a newly stable local oscillation mode. Besides, the fluctuation of wind speed and the increase of stiffness coefficient of the shaft would decline the stability of the oscillation modes slightly. In addition, the increase of the penetration of wind power would lead to the decline of the stability of each oscillation mode, especially for the inter area oscillation mode. As a result, the parameter of the damped oscillation can better describe the characteristics of the small signal stability of wind power.