Improved Reactive Power-voltage Droop Control Strategy And Incremental Reactive Power Output Optimization Of Wind Farms With DFIGs

The reactive power distribution in wind farms depends on the power flow modeling of doubly-fed induction generator?DFIG?,and is affected by factors such as wind speed,reactive power margin,and electrical distance between the the public coupling point?PCC?and each DFIG.Therefore,it is necessary to comprehensively consider the stator voltage of each DFIG and the active power loss in wind farms.The existing dispatch scheme for the allocation of the reactive power of the wind power system is realized on the wind farm level,which needs to be further extended to each DFIG to improve its feasibility.For the power system with the wind power integration,its mathematical model has the high nonlinearity and optimization objectives may be adopted.Therefore,it is of great significance to dispatch the reactive power outputs among the DFIGs.The complete model of DFIG-based wind farm is studied in this paper.The main contents of the research are listed below:?1?To address issues related to the control of large-scale wind farms,a bi-level reactive power optimization model of wind power system is established.The reactive power demand is determined on the grid level and the reactive power sharing among the DFIGs is determined on the wind farm level.In order to solve the problem of impedance inconsistency between wind farms and PCC,an optimal reactive power-voltage droop control strategy based on active power loss and reactive power margin of wind farms is proposed.And the weight coefficients of the objective functions are determined based on the reactive power margin of wind farms.?2?Aiming at the problem that the inconsistent operation parameters of wind farms and DFIGs affect the selection of droop coefficient,a reactive power-voltage droop control strategy incorporating variable droop coefficient is proposed,and the droop coefficient is adjusted according to the change of wind speed.According to the reactive power margin and electrical distance from PCC of the DFIG,the indicator of the reactive power imbalance is proposed.On the grid level,equivalence of the loss is considered in the model of wind farms.The LBFGS-TR algorithm is adopted to solve the reactive power dispatch scheme of the wind farms and DFIGs.?3?To deal with the problem of high dimensions and nonlinearity in the reactive power dispatch on the wind farm level,a multi-object optimization method for the dispatch of the reactive power incremental distribution among wind farms based on the2^nd order sensitivity is proposed.According to the voltage fluctuation of the PCC,the DFIG reactive power distribution coefficient is proposed,and the incremental model of the the wind farm is established to reduce the number of variables.The 2^nd order sensitivities of the active power loss and stator voltage in the wind farm to the power outputs of DFIGs are used to reduce the nonlinearity of the optimization model and improve the calculation speed.NSGA-II algorithm is used to obtain the Pareto front and then the compromise solution of the multi-object optimization is proposed based on the evaluation indicator of the reactive power margin.