Research On Modeling And Dynamic Characteristics Of Doubly Fed Wind Turbine Generators Connected Into Power Grid

The traditional energy shortage, environment pollution are more serious, so the transformation of global to safe, reliable and environmental sustainable energy system is imminent, which brings wind power an important opportunity for development. In recent years, China has become the wind first state of the new installed capacity. However, with the wind scale continuously increases, the influence of wind farm on the grid can not be ignored. Doubly-fed type wind-driven generator is currently one of the mainstream of wind power generation, but wind speed'randomness causes power fluctuation and influences the power quality and system stability,and these require further studies. Therefore, based on the actual project, modeling, dynamic characteristics , influences on stability and power quality of DFIG wind generators were studied.In the modeling aspect, firstly, different models used to study different problems were summarized.Then the common control strategy was analysed and it could only be used in the port voltage relatively stable circumstances with good control effect. Secondly,the generally used control strategy was improved, and a new control strategy was presented, which can automatically compensate the reactive power needs according to the system, Additionally, the model was verified based on PSCAD/EMTDC platform. Again, considering that the parameters and control strategy of wind power generation can not easily obtained, the average model in Matlab/Simulink Platform was choosed,and was used to discuss the Security Capacity of an actual network based on its consistency dynamic fault characteristics with the model in PSCAD/EMTDC.In the dynamic performance and the influence on network aspect, firstly, the port characteristics of wind generator in normal and failure situation were studied.Then, the effect of adding Crowbar to improve LVRT of the wind generator was discussed,and the net side converter control strategy should be improvemented to reduce the absorption of reactive power from the grid. The former task provides theory basis for the thorough grasp of the wind generator operation characteristics.Secondly, based on the PSCAD/EMTDC plantform, the simulation model was built in an actual local network containing wind farm.From normal and fault two angles, considering wind speed, wind farm capacity, clearance time, fault symmetry and dynamic load eta., the influences of a wind farm on the network's voltage stability and power quality were studied.Through these studies, some significant conclusions were obtained,which is the foundation for further studies.