Research On Small Disturbance Stability Of Power System Integrated With Large Scale Wind Farms

With the integration of ten-million megawatt-class wind power bases into grid in China,the wind power penetration rate in power systems has increased sharply.However,the high wind power penetration rate not only reduces the system inertia,but also may adversely affect its damping characteristics,and then brings a serious threat to the actual power system on its safe and stable operation.Therefore,it is an urgent problem to study the influence of large wind power on the power oscillation and damping characteristics of the system.In the previous literatures,the wind turbine models used are mostly user-defined models,and the validities of the models are not guaranteed,so the reliabilities of the results are reduced;besides,most of the traditional research methods focus only on the influence of the original oscillation modes of the system,and less research are conducted on power oscillation modes that caused by the wind farms.For the above problems,the eigenvalue analysis method,combined with time domain simulation and prony analysis are carried out to study the power system integrated with large-scale wind farms,and the followings are the research contents and results:(1)The modeling principles and modal structures of the general dynamic model(GDM)of the Western Electricity Coordinating Council(WECC)type ? and type ? wind turbines are expounded in detail,and a brief comparison of the differences between the two generations models is performed by simulation.Besides,the improvement section of the second generation GDM is pointed out,and the necessity of applying the second generation GDM is clarified.(2)Based on the GDM of the second generation type ? wind turbines,combined with small disturbance eigenvalue analysis,time domain simulation and prony analysis,it is revealed that a type ? wind turbine/farm will produce a pair of high frequency power oscillation modes,which are strongly correlated with the control variables of the wind turbines by verifying the participation factors.With the increase of wind power permeability,modal dampings of these control modes decrease,and finally drive the system power oscillation,resulting in small disturbance instability of the system.The research results show that with the wind power permeability increases,the power system may produce a new stable form,that is,wind turbine control mode stability,which is different from previous power angle stability problem.(3)Based on the GDM of the second generation type ? wind turbine,it is found that integration of a type ? wind turbine/farm introduces a pair of common modes "wind turbine electromechanical oscillation modes" related to the power angle and speed of the wind turbine in power system.This new type of "wind turbine electromechanical oscillation modes" spread to the grid through the converter,and can produce a strong interaction between wind turbines.It should be noted that these modes are only related to the power angle and speed of the type ? generators,but are weakly related to the electrical control of the converter.With the increase of wind power permeability,the dampings of "wind turbine unit electromechanical oscillation modes" gradually become weak,and finally cause the small disturbance instability of the power system.