Research On Reactive Power Coordinated Control Of Doubly Fed Induction Wind Power Generator Unit Under Grid Fault

As a clean and renewable energy resource,wind power generation has broad development prospects,and variable speed wind turbine based on Doubly Fed Induction Generator is one of the most popular generators at present.Although DFIG is very sensitive to power grid faults,esp ecially under faults which lead to voltage failure,DFIG has the ability to adjust reactive power dynamically by outputting reactive power from stator side and grid side converter to grid.Therefore,the DFIG's reactive power regulation capability can be f ully excavated to help improve the low voltage ride through(LVRT)capability of wind turbines.On the basis of that,this paper presented two ways to ensure the LVRT of wind farms under faults.On one hand,coordinating DFIG and reactive power compensatio n devices can provide reactive power to support the grid voltage.On the other hand,the reactive power regulation capability of DFIG can be applied to the wind power system with rotor series resistor circuit.This paper has made comprehensive and intensiv e research to deal with the above problems,the concrete work is as follows:(1)According to the mathematical model of DFIG in the synchronous rotating coordinate system,the control strategy of rotor side converter is improved considering the dynamic variation of stator flux and excitation current.Meanwhile,the control strategy of the grid side converter is improved in order to balance its input power and the output power.(2)After analyzing the reactive power capability and the reactive power limit of stator side and grid side converter of DFIG,under constant voltage control,three typical distribution modes of reactive power reference instruction between the rotor side converter and the grid side converter are simulated and compared,which help to select the optimal reactive power coordination control strategy.(3)On the basis of taking full advantage of DFIG's reactive power control capability,two kinds of reactive power coordinated control schemes are proposed to improve the fault ride through capability of wind power system,of which,one is a reactive power coordination control method combining DFIG with STATCOM and the other is a reactive power coordination control method based on rotor series resistor circuit.The simulation results verified the effectiveness and feasibility of the proposed reactive power coordination control schemes.(4)Finally,the simulation model of grid-connected DFIG system is set up on the Matlab/Simulink simulation platform,and the above work is researched on this basis.