Research On Reactive Power Optimization And Control Strategy Of Decentralized Wind Turbine Connected To Distribution Network

Wind power,as the most promising new energy for large-scale development and commercialization,has been installed in large quantities.Wind power accumulative installation of China ranks first in the world.In the various installation methods of wind power,the decentralized wind farm has been widely paid attention to the advantages of local conditions,general access to the end of low voltage distribution network,and easy to be eliminated in place.It is a kind of power grid friendly power generation mode.However,it is also easily affected by the weak network characteristics of the power grid,and the commonly used Doubly-Fed Induction Generator(DFIG)model itself needs to absorb the reactive power from the power grid which further worsens the voltage quality of the distribution network.This paper studies the reactive power optimization and control strategy of distributed wind turbines connected to the distribution network.The system level reactive power optimization and distribution of decentralized wind farms from the point of view of distribution network and the reactive power control strategy of single DFIG from the perspective of converter are studied.Firstly,this article discusses the reactive power limit of DFIG system based on the reactive power limit of stator side which was based on the considerations with current constraint and static stability limit,and the reactive power capacity of the grid side converter(GSC)which further explored the limit of reactive power output.The conventional control method of unit power factor operation was broken,which laid a theoretical foundation to participate in the reactive power regulation of grid system.In order to realize the limit reactive power operation,DFIG reactive power control strategy based on dq rotary coordinates is analyzed,designed and verified.Based on the shortage of basic particle swarm optimization(PSO),this paper proposes an improved PSO algorithm to solve reactive power optimization of decentralized wind farms.The reactive power optimization model is studied by obeying the reactive power limit of DFIG.The reactive power distribution principle of the stator side and the grid side converter is given,and the improved PSO algorithm is used for reactive power optimization which uses the sum of the net loss and average voltage deviation as the objective function.The reactive power demand of the system is solved according to the deviation of the node voltage and the reference value.Considering the geographical location of the distributed wind farm,the wind resources and the power grid lines,the reactive power distribution of each DFIG in the wind farm is studied.The simulation results show that the method can greatly reduce the network loss and improve the voltage stability of the system.Finally,according to the above single DFIG reactive power instructions,the reactive power control strategy is studied.The traditional PI control system based on dq rotating coordinates has a serious coupling problem,which can not achieve accurate tracking of reactive instruction,and the frequency adaptation range of PR control based on static coordinates is limited,and it has hidden danger of stability.In this paper,an open loop current controller structure under static coordinates is studied to achieve accurate and fast tracking of reactive power commands.The principle of the controller is analyzed,and the process of parameter design and selection is given.It is applied to the control of DFIG grid side converter to realize the accurate tracking of the reactive power instruction on grid side.