Research On Frequency Stability Control Strategy Of Large-scale Wind Power System After Grid Connection

With the deepening of energy reform,the demand and installed capacity of green renewable energy are increasing day by day.As the pioneer of renewable energy,the increase of military wind power grid connection has brought a direct impact on the frequency stability of the power system.Because of the inverter structure inside the wind turbine,the rotor speed is decoupled from the system frequency,and it does not have the inertial response capability similar to the traditional synchronous generator,so it cannot delay the frequency fluctuation by changing the rotor speed when the system power changes.At the same time,because the wind Power group mostly adopts the maximum Power Point Tracking(MPPT)operation,it does not have standby Power and cannot provide additional Power support when the system Power is short.This series of characteristics determine that wind power grid connection without improvement of frequency stability control will inevitably increase the difficulty of frequency stability regulation of the whole power grid,which is not conducive to the stable operation of the power system.Therefore,it is of great significance to study and improve the frequency stability regulation ability of wind power after grid connection for the stable operation of the power system and the increasing consumption of new energy.In this paper,Doubly-fed Induction Generator,which accounts for the largest proportion of wind power and is widely used,which is taken as the research object.In the unit control layer,according to own DFIG operation characteristics,the operation condition was setting,and relying on the working condition of three respectively formulate the corresponding lightening control measures,improved variable coefficient droop control,the additional inertia at present commonly used control,will be introduced to the wind speed fluctuation and change of the frequency droop control coefficient values,effectively improve the droop.According to the working condition of the whole set the virtual variable coefficient of inertia control strategy,combined with the unit to control the level of comprehensive frequency stability control measures,in view of the DFIG participating in frequency control aspects of the current available methods were analyzed,and the rotor kinetic energy control and alternative method for lightening two mainstream means,in the middle and lower wind speed using the rotor speed control,the operating point back to the standby power;In high wind speed section,the control system of pitch Angle is used to reduce wind power capture of wind turbine and realize power reserve.With the addition of droop control and virtual inertial control,DFIG can simulate the inertial response capability similar to that of the synchronous machine.Based on the traditional pitch Angle control,the pitch Angle control loop was improved,and the frequency variation of the system was introduced into the pitch Angle control mechanism.The backup power was linked with the frequency,and the above control measures were integrated into a comprehensive frequency stability control strategy.The effectiveness of the proposed integrated frequency stability control strategy is verified by simulation with a practical grid model that includes large-scale wind power access to base load as hydropower.In the wind farm,the paper analyzes the different penetration of wind power grid reduces the system frequency stability,study and formulate the field unit active measures to control the distribution and coordination of frequency parameters according to the size of the flight reservation point input speed of the field units can be divided into type I lower the wind generator units and class II,high wind speed of the two types of units take different output distribution coefficient and the differential coefficient,the wind farm in low wind speed unit in maintaining the stability of its startup phase running at the same time appropriate for frequency modulation,high wind speed in units of frequency control.It improves the frequency regulation ability and operation stability of the wind farm as a unit,and reduces the frequency regulation pressure of the hydroelectric units in the same area.By establishing a wind farm model with class I units as the main unit and class II units as the auxiliary unit,the simulation analysis is carried out in the actual regional power grid model.