The Study Of Large-scale Wind Power Effect On Power System Out-of-step Oscillation

With the national interconnected power grid expanding,once the accident of out-of-step oscillation appears and effective measures are not taken,the scope involved will be multiplied and even the whole interconnected power grid.Distribution characteristic of the oscillation center is the foundation of the effective configuration separation device,to solve the problem,experts at home and abroad have conducted in-depth research and obtained great achievements.In recent years,with the scale of wind power increasing,the power system stability is affected by wind power more and more obvious.The active power output of wind power is intermittent and randomness,and changes frequently;the changing of active power fluctuation may lead to voltage control characteristic and dynamic reactive power compensation change corresponding;moreover low voltage ride through and high voltage protection feature of wind power generator,which may cause the wind power supply under the relevant fault be more easier to take off the grid than conventional power.All these factors make the wind power feature show a certain variable property,which will inevitably affect the oscillation center distribution and lead to the oscillation center migration in actual grid.But there is no research report about the impact of wind power integration on power system out-of-step oscillation.This paper reviews the research status of out-of-step oscillation problem,introduces the DFIG into the equivalent of two machines system,and analyzes the distribution as well as migration regularity of out-of-step oscillation center.The simulation system near to actual power grid is established,and how the change of wind power output affects the out-of-step oscillation is analyzed.The correctness of above conclusions is verified based on the actual Northwest Power Grid.The main contributions of this paper are as follows:1)In the equivalent of two machines system,the oscillation center offset is mainly caused by the unequal of voltage amplitude E_M,E_N and the offset close to the lower voltage amplitude.The doubly-fed induction generator is cited into the equivalent of two machines system,Voltage of wind power generation shows the nature that the doubly-fed induction generator affects oscillation center of system.While the voltage changes according to the variety of wind turbine parameters.2)Based on the equivalent of two machines system,the simulation system model closest to the actual situation of power grid is built.Analyzing how the change of wind power output affects the out-of-step oscillation from the perspective of simulation.The simulation results are showed following:that the wind power output change will lead to the system out-of-step oscillation quantity increase,even the original normal system will be infected,as well as out-of-step oscillation center will migrate to the side of higher output of wind power.The armature fan has strong coupling with power grid,which can absorb the oscillation energy and slow down the out-of-step oscillation process.While the doubly-fed induction generator is weak coupling with power grid,and has no effect on the out-of-step oscillation.The position of dynamic reactive power compensation has enormous influence on of out-of-step oscillation,the SVC access to out-of-step oscillation center will make oscillation deteriorate,but the SVC access to both ends of the equivalent system can effectively alleviate the out-of-step oscillation.3)Based on the northwest actual power grid,the paper studies and verifies that how the wind power changes and the system dynamic reactive power compensation affects the grid out-of-step oscillation.Research shows that wind power fluctuation destroys the original out-of-step oscillation mode in northwest power grid,and a large number of units out of step appears after system splitting;Under the condition of wide fluctuation of wind power in Xinjiang and Gansu province,the out-of-step oscillation center in Northwest power grid migrates to the wind power fluctuation side,and new oscillation mode appears in the system.Under the condition of full wind power output in Northwest power grid,when SVC accesses to control high voltage bus 750kV of Qiaowan station and Xian station,out-of-step phenomenon does not appear in a large number of the unit after system splitting,and multi-frequency oscillation is restrained.The above results are consistent basically with the simulation.