中文摘要：

为了研究直驱永磁风电场并网后对电力系统小干扰稳定性的影响，建立了直驱永磁同步风力发电机组的数学模型，采用特征值分析法，以无穷大系统和IEEE3机9节点系统为例进行分析，并且对系统小于扰稳定裕度进行了讨论。算例分析表明：当风电场出力增加时，与风电场强相关的振荡模式的阻尼比呈现出减小的趋势，对与系统中同步发电机组强相关的振荡模式影响不大，当风电场出力增加到一定程度时，系统小干扰不稳定。最后，通过李雅普诺夫直接法验证了结论。

英文摘要：

In order to study the impact of grid-connected direct-driven permanent-magnet wind farm on power system small signal stability, the mathematical model of direct-drive permanent-magnet synchronous wind turbine is established. By using eigenvalue analysis method, an infinitive bus system and an IEEE 3-machine 9- bus system are investigated respectively, and then the small signal stability margin is discussed. The analysis of cases shows that the damping ratio of oscillation modes strongly related to wind farm shows a decreasing trend with the wind farm output increasing. The influence of wind farm on oscillation modes strongly related to other synchronous generators is considerably weak. When wind farm output increases to a certain extent, power system becomes unstable for the small signal. At last, Lyapunov direct method is employed to verify the conclusions.