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Reactive Power Limit of Variable-Speed Constant-Frequency Wind Turbine SHEN Hong, WANG Wei-Sheng, DAI Hui-Zhuc (China Electric Power Research Institute, Beijing 100085, China) Recently, with the rapid development of wind power, the variable-speed constant-frequency wind turbine has become the main type in the global market. Although the performance of variable-speed constant-frequency wind turbine is much better than fixed-speed wind turbine, it is still an impact to the grid while it is integrated into the power system for variation of wind speed, therefore it is necessary to study the new type of wind turbine's integration characteristics. The generator of the variable-speed constant-frequency wind turbine is doubly-fed induction machine, its rotation speed and reactive power in stator side can be adjusted according to their control scheme. In paper [1,2], the steady state model based on d-q frame was studied and established, the objective of rotation speed control is optimal capacity factor, and the reactive power control includes two types of control: constant power factor control and constant voltage control. Wind farm is usually sited in remote area, where the grid is weak and the requirement of reactive power to keep the voltage level is very urgent. When variable-speed constant-frequency wind turbine under constant voltage control is installed there, if the reactive power needed to be produced from the generator exceeds its reactive power limit, the wind turbine will stop because of winding heating, on the other hand, since the reactive power produced by the wind turbine can not satisfied the requirement by the grid, the voltage will increase or decrease, in serious cases, will result into voltage instability. In paper , the reactive power limit of variable-speed constant-frequency wind turbine was studied, but only the problem of the steady state operation region of the reactive power and the active power in stator winding is researched. In this paper, a steady state model of the variable-speed constant-frequency wind turbine was established. On the basis of this model, an approach to calculate the reactive power limit of variable-speed constant-frequency wind turbine was presented, this approach can work out the steady state operation region of the total active power and reactive power injected into grid, which also takes account of the rotation speed control of the wind turbine. Finally, an 800kW variable-speed constant-frequency wind turbine is used to be calculated as sample.  Muljadi E, Butterfield C P. Pitch-Controlled Variable Speed Wind Turbine Generation [M]. IEEE Industry Applications Society, Annual Meeting, Phoenix, Arizona, 1999  Refoufi L, Zahawi B A T Al, Jack A G. Analysis and Modeling of Steady State Behavior of Static Kramer Induction Generator [J]. IEEE Transactions on Energy Conversion, 1999, 14(3): 333-339 Tapia A, Tapia G, Ostolaza X, Fernández E, Saenz J R. Modeling and Dynamic Regulation of A Wind Farm. Power Electronics Congress, 2000. CIEP 2000. VII IEEE International, 2000 Page(s): 293 -297 Wang Wisheng – Curriculum Vitae Mr. H. Shen was born on Aug 22, 1971 in Heilongjiang Province, China. He received his Bachelor degree and Master degree at Northeast Institute of Electric Power in July 1993 and April 1999, respectively, both in Electrical Engineering. Now, He is a doctoral student in China Electric Power Research Institute. His areas of research interest are power system and wind power generation. Dr. W.S. Wang (member of IEEE) was born on Mar 27, 1968 in Shanxi Province, China. He received his Bachelor degree and Master degree at Xi’an University of Technology, Doctor degree at Xi’an Jiaotong University, in July 1990, July 1993 and Dec. 1996, respectively, all in Electrical Engineering. Now, He is a senior engineer in China Electric Power Research Institute. His areas of research interest are power system and wind power generation. Prof. H.Z. Dai was born on Jan. 12, 1939 in Jiangxi Province, China. She graduated from Department of Electrical Engineering, Tsinghua University in July 1962. From 1981 to 1983, she worked in Leihigh University and Cornell University, USA as a senior visiting scholar. Now, She is a professor in China Electric Power Research Institute. Her areas of research interest are power system and wind power generation.