Study On Self-starting Control Strategy Of Large Wind Farm With Energy Storage

When a large-scale power outage occurs in the power grid,it is necessary to restore the power grid to normal conditions through black-start as soon as possible.Generally,hydropower plant is the ideal choice to undertake the black-start power supply.However,due to the lack of water resources in some areas of China,more abundant wind energy resources can be selected to undertake the black-start power supply.Since wind turbines do not have self-starting capabilities,it is necessary to configure large-capacity battery energy storage devices for wind farms to achieve self-starting.When a large wind farm with energy storage is self-starting,it is necessary to charge the power equipment under no-load,and no-load charging will inevitably produce certain overcurrent and overvoltage problems.These problems may cause the self-starting of the wind farm and the black-start to fail.After the self-starting is completed and connected to the grid,other electric fields are driven,the power generation capacity in the power grid is not large,and the structure of the power grid is unstable.The overall power grid is in a weak power supply and weak connection condition.The input of other electric fields and loads will cause certain disturbances in the system,the problem of power oscillation in multiple frequency bands cannot be avoided.These problems may cause the black-start to fail and the power grid cannot be restored in time.Energy storage device has the advantages of fast power response and convenient control.If these advantages can take effect,the safety and reliability of wind farm self-starting can be effectively improved,and at the same time,the damping control of the multi-band oscillation in the weak power grid can be performed.This article mainly conducts the following research:(1)Analyze and establish the mathematical model of permanent magnet direct drive wind turbine and energy storage device.A simulation model for wind turbines based on MATLAB/Simulink is established,including mechanical part module,electrical part module and control module.A simulation model of the energy storage device is also established,including the electrical part module and the control module.(2)The excitation inrush current and the corresponding inrush current during the no-load charging of the transformer during the wind farm self-starting are analyzed.Different suppression strategies based on energy storage devices are designed for the box-type transformer of the wind turbine and the main transformer of the wind farm.Design a zero-start boost control strategy for energy storage devices with no-load charging of multiple sets of box-type transformers.A simulation is designed to verify the state of excitation inrush under different starting methods.For the no-load charging excitation inrush current problem of the main transformer,the energy storage device is designed to absorb excitation Inrush control strategy.A simulation is designed to verify the absorption effect of the energy storage device on the excitation inrush current.(3)Analyze the over-voltage problem of no-load transmission line charging when the wind farm is connected to the grid,Analyze the generation mechanism of over-voltage during closing operation.Design the no-load closing over-voltage suppression method based on energy storage device,and realize the no-load transmission line’s head voltage gradually increases to suppress the line’s overvoltage.A simulation is designed to verify the overvoltage suppression effect of the closing operation,and compared with the closing resistance suppression strategy.(4)Analyze the multi-band oscillation existing in the weak power grid at the beginning of the black-start.Design a method to achieve multi-band damping control through the control of energy storage devices.The multi-band damping control strategy of the energy storage device is used to dynamically inject active power and reactive power into the power grid to suppress multi-band oscillations in the weak power grid.A simulation is designed to verify the effectiveness of the multi-band damping control strategy.