Research On Loss Optimization Control Strategy Of DFIG Wind Farm

As fossil energy becomes scarce,people are gradually turning their attention to renewable energy,among which solar energy and wind energy are the most widely used,wind power is now becoming one of the fastest growing renewable energy source in the world.In the most of the wind power generation,doubly-fed induction generation(DFIG)is widely used for its merits,such as decoupled active power and reactive power control,higher wind energy usage rate,better system stability and wider operating range.With the wide application of large megawatt wind turbines(WTs),as well as the characteristics of large scale wind farms with a wide geographical area and a large number of WTs,transmission line losses inside wind farms will become more obvious.The increase of active power loss will lead to more consumption of electrical energy in the process of transmission and decrease the transfer efficiency.This paper propose a reactive power control strategy to minimize the total losses of wind farm.Firstly,this paper researches the basic characteristics of wind power generation.Based on the structural characteristics of variable speed constant frequency DFIG,this paper establishes the mathematical model of DFIG,and then induces the stator flux directional vector control and network-side voltage directional vector control of DFIG to realize the decoupled control of stator-side reactive power and grid-side reactive power.And the stator-side reactive power control model and the grid-side reactive power control model are established.And the discrete state reactive power control model of the entire wind farm is derived.According to the loss calculation formula of wind farm equipment,which include generator loss,converters loss,filter loss and network loss,this paper obtains the quadratic programming formulate of various loss with respect to reactive power by linearization process.The model predictive control(MPC)is used to establish the objective function of minimum total active power loss value of DFIG wind farm,and the reactive power state value and input value in a period of future prediction period is predicted,and obtains the reactive power control value of each wind turbine in the wind farm by rolling optimization and solving the objective function.The sum of the reactive power control value is the same as the total reactive power demand of wind farm to achieve power tracking.And finally establishes the simulation model and compared with the reactive power control strategy of minimum transmission line loss,which proves the efficiency of the proposed control strategy.Model predictive control(MPC)uses centralized calculation method,which will increase the computation burden and communication cost,so an alternating direction multiplier method(ADMM)loss optimization control strategy is proposed in this paper.Establish central controller and multiple wind turbine controllers,the central controller optimizes the transmission line loss,and each wind turbine is equipped with a wind turbine controller to independently optimize the internal loss and converter loss of the wind turbine.Finally,this paper establishes the simulation model,and compared with the reactive power control strategy of minimum transmission line loss,simulation results confirm the effective of the presented control strategy.