Optimal Control Of The Active And Reactive Power For The Doubly Fed Induction Generator-based Wind Farm

Due to its high reliability,small capacity of converter,mature technol ogy,stable and reliable quality,doubly fed asynchronous wind power generation system has been the mainstream in the wind power generation system.The doubly fed induction generator(DFIG)based wind turbine can decouple the control of the active and reactive power by controlling the excitation current of the rotor independently,which can adjust the reactive power rapidly and continuously,and provide the reactive power support for the power system.Therefore,the DFIG-based wind turbine can be used as the reactive power compensation power of the power system,participate in the reactive power compensation of the system,and regulate the voltage of the system.In this paper,a centralized active and reactive coordinated control strategy and a distributed active and reactive coordinated control strategy are proposed for the active and reactive power control of doubly fed wind farms.The specific contents of this paper are as follows:On the basis of linearized optimal power flow model,a centralized active a nd reactive power coordinated control strategy for doubly fed wind farms to minimize the power loss is proposed in the paper.The strategy can reduce the power loss of the wind farm,include the copper loss and converter loss of the doubly fed generators,and the network loss of the doubly fed wind farms.It can also track the active and reactive power dispatch commands from the dispatch center,which satisfies the needs of the doubly fed wind farms.By optimally dividing the reactive power outputs between the stator and the grid-side converter,the centralized control strategy can reduce the power loss of the DFIG-based wind turbines.Then,the power loss optimal problem of the doubly fed wind farm is reconstruct into an optimal power flow model based on the linearized power flow equations,so as to reduce the network loss and the power loss of DFIG-based wind turbine,and lessen the cumulative fatigue effect of the converters and other equipments in the doubly fed wind farm.The simulation results show that the centralized optimal control strategy proposed in the paper can reduce the total power loss of the doubly fed wind farms on the premise of tracking the active and reactive power dispatch commands.Combining the alternating direction method of multipliers(ADMM),the centralized active and reactive power control model is reconstructed into an ADMM-based distributed active and reactive power control model in the paper.Each node in the doubly fed wind farm corresponds to an independent sub-controller.Iterative solution is adopted by the sub-controller to independently compute the objective function of the corresponding node.The local communication occurs between two adjacent sub-controllers to exchange the iterative update values of the local variables,which ensures the global consistency of the solutions to sub-controllers,guarantees the global optimal of the solution,and avoids the local optimal.The action of the centralized problem solves in a totally distributed way can avoids the use of a central controller and without loss of the optimum of the primal centralized problem,which can also reduce the cost of the communication in the doubly fed wind farm,lessen the computation burden and storage requirements of the controllers,and protect the privacy security of the DFIG-based wind turbines.The simulation resluts prove that the distributed active and reactive power control strategy can solve the centralized problem in a totally distributed way without loss of the optimum of the primal centralized problem.It can also realize the control target of the distributed control in multiple operation scenarios of doubly fed wind farm.