Research On The Control Strategy Of Low Frequency Oscillation Damping In Interconnected Power System With Large-scale Wind Farm

With the construction of global energy Internet,the scale of interconnected power grid in the world is in a rapidly developing stage.Large-scale wind farm is added to interconnected power grid,its volatility,intermittence and randomness not only increase power system peak regulation pressure,but also affect the safe and stable operation,especially the large capacity of transmission line and weak network directly may lead to low frequency oscillation phenomenon.In this thesis,the influence of large-scale wind power on the low frequency oscillation of power system based on double-fed induction generator(DFIG)is investigated,and an effective wide-area damping control strategy is proposed.First of all,the system structure and working principle of doubly-fed wind power generator are expounded,and the mathematical model of doubly-fed wind turbine is established.The linear mechanism and nonlinear mechanism of low frequency oscillation of interconnected power grid and the main analysis method based on modal and measurement data and the low frequency oscillation suppression measure are summarized and analyzed.The influence of the wind farm on the damping performance of the two interconnected power systems in different regions is deduced theoretically.Then,the system structure of the interconnected power grid with large-scale wind farm is designed,and the control structure of the rotor side with damping controller used in the DFIG wind farm is studied.As to the interconnected power grid with the wind farm,the test signal method and the prediction error minimization method are combined,meanwhile,a whole wide-area damping control method based on phase compensation and root locus method is proposed to achieve oscillation monitoring,the system mode identification and the design of damping controller.It can effectively monitor and suppress the low frequency oscillation in the interconnected power system.And the case study is carried out by using eigenvalue analysis and time domain simulation in the interconnection system,which verifies the validity and correctness of the strategy.Finally,a simulation model of interconnected power grid based on the platform of Matlab/simulink with large-scale DFIG wind farm is proposed.The wide-area damping performance of the interconnected system is studied and analyzed in three aspects during the application of wide-area damping control strategy,including the selection of feedback signal,the added position of the controller and the choice of the excitation signal in the test signal method.On the other hand,the influence of the wind speed,wind power output and wind power transmission distance on oscillation mode of DFIG wind farm are studied and analyzed.It is found that the adding of DFIG wind farm will change the original structure of interconnected system and more or less affect the oscillation mode of the system,which makes the damping characteristic of the interconnected system become more complicated and changeable.