Research On Control Strategy For Grid-connecting Converter Of Wind Power Generation System Under Abnormal Grid Condition

As a renewable and clean energy,wind energy has been paid more and more attention by the governments of all countries?Direct drive wind power generation system has the advantages of simple structure,high utilization rate of wind energy,flexible control of grid connected power and low voltage ride through capability.In this paper,the control strategy of direct drive permanent magnet motor wind power system under abnormal grid conditions is studied.In this paper,the operating principle of the main components such as the permanent magnet motor,the machine side converter and the grid side converter are studied.And the mathematical model is established in different coordinate systems.Based on the principle of vector control,the control method of the machine side and the grid side converter under the traditional strategy is studied.The object is controlled by the machine side converter to control the DC voltage and the stator voltage,and the active power of the generator and the reactive power of the network-side are controlled by the network-side converter.A new control strategy is proposed by using PI controller to control the stable operation of wind turbine.Secondly,a new coordinated control strategy of permanent magnet motor wind power system is put forward when the grid voltage drops.The control system is controlled by the machine side control DC bus voltage and the grid side control power,and the pitch angle control and the DC unloading unit are used as auxiliary control.Making use of the two different response speed,to optimize the cutting process.So that the DC unloading circuit in the DC bus voltage over time,in the pitch angle to play a substantial role in the timely exit.The strategy which makes the voltage fluctuation of the DC bus voltage smaller and improves the low voltage ride through capability of the wind power system can solve the problems of slow cooling of DC bus and slow response of the pitch angle.In the case of unbalanced power grid voltage drop,this paper takes the suppression of the 2 frequency fluctuation of DC bus as the control target.A double closed loop control strategy is proposed to control the positive and negative sequence currents in the positive and negative sequence rotating coordinate systems.The parameters of the positive and negative sequence current instructions are compensated to improve the zero error tracking of the DC voltage o f the grid side converter,and the 2 ripple of the voltage is suppressed.Finally,the control strategy is verified by Matlab/Simulink software platform,The simulation results show that the proposed control strategy can effectively enhance the adaptability of the permanent magnet motor to the power grid and the low voltage ride through capability effectively.