Research On The Large-scale Wind Farm Modeling And Reactive Power Optimization Control

The increasing penetration of wind power and growing size of the wind farm have significant impacts on the system operation due to the stochastic and fluctuant nature of wind,and introduce technical challenges to voltage stability.Since large wind farms are mainly located in areas far from load centers,the short circuit ratio is small,and the grid at the connection point is weak.The voltage fluctuation caused by the intermittent power of the wind farms is quite large.Moreover,the grid disturbance may cause cascading trip of wind turbines(WTs).Therefore,modern wind farms are required to meet more stringent technical requirements of voltage support specified by system operators.The requirements include reactive power capability of the wind farm and voltage operating range at point of common coupling(PCC).Firstly,the basic structure and power flow characteristics of doubly fed induction generators(DFIGs)are briefly stated,and the control system of rotor-side converter(RSC)and grid-side converter(GSC)is analyzed.On the basis of these principles,we make researches on the requirement of grid voltage control as well as the reactive power control approaches of DFIG.According to the reactive power constraints of the RSC and GSC,the reactive power output limits of DFIGs under different active outputs are deduced in details.Then this paper analyzes the active power loss of the wind farm collector system including transformers and transmission lines.Secondly,this paper analyzes the reactive power demand of PCC and uses the secondary adjustment method to determine the reactive power compensation of PCC.In addition,in order to meet the reactive power demand of PCC,an optimal reactive power dispatching(ORPD)method is proposed on the basis of proportional dispatching strategy of reactive power.The purpose is to minimize active power losses in a large-scale wind farm(WF),including transformers and transmission cables in collector system.Moreover,this paper employs an improved genetic algorithm(GA)to obtain the optimal solution,and the penalty functions are adopted to deal with the constraints.Aiming at the problem of time-consuming iterative computation of GA,this paper will establish an ORPD database and store the ORPD references to achieve fast reactive power dispatching of the WF.Finally,the system study is performed using the MATLAB/Simulink.According to different operating conditions,the test is carried out by using the traditional proportional scheduling strategy and ORPD strategy,respectively.The simulation results show the proposed ORPD strategy based on GAs has an obvious effectiveness on minimizing the active power losses in collector system of a WF.