Research On Control Strategies For Wind Power Generators Participating In Secondary Frequency Regulation To Power Grid

As a kind of clean,economic and abundant new energy,wind energy is increasingly widely used.In some area,over 20% of the penetration ratio at the end of power grid makes it hard for synchronous generators maintaining synchronous operation and synchronous generators suffer from great frequency regulation pressure after large-scale wind power gets injected into power grid.At present,primary frequency regulation of wind power has been studied at home and abroad,but there are few researches on secondary frequency regulation of wind power.Secondary frequency regulation can improve system frequency to the normal value,which is of great significance for undifferentiated frequency regulation to power grid.So it is essential to analyze primary and secondary frequency regulation characteristics of the high-penetration-ratio system and adopt some frequency regulation strategies when wind power generators participate in the frequency regulation to power system.In this paper,the over-speed load reduction method,virtual inertia control and variable pitch angle operation mode of doubly-fed induction generator(DFIG)are studied,the method of wind turbine participating in primary and secondary frequency regulation to power grid is improved and the corresponding frequency response control module is built.In low-wind-speed section,the primary frequency regulation method based on over-speed load reduction method and integrated virtual inertia control is used to enhance the frequency stability of power system.In high-wind-speed section,the secondary frequency regulation method based on pitch control and improved PI control is used to restore power grid frequency to the normal value.In this paper,three working conditions of wind turbine operation are set up and the concepts of Frequency-regulation Penetration Ratio and Frequency-regulation Depth are presented.And then this paper comparatively analyzes the frequency regulation characteristics of power system under different frequency-regulation penetration ratio or depth in the same model without changing parameters of power grid upon 40% invariable wind penetration ratio model and proposes three control methods of ‘Utilizing Maximum Primary Frequency Regulation Penetration Ratio’,‘Taking Combined Action of Primary and Secondary Frequency Regulation’ and ‘Increasing Frequency Regulation Depth’,which can give full play to DFIG’s frequency regulation capability.On the basis of frequency regulation characteristics of DFIG and three control methods,this paper proposes a primary frequency regulation strategy of ‘Optimizing Adjustment Coefficient’ in low wind speed section to improve the utilization of DFIG reserve power.In high wind speed section,a secondary frequency regulation strategy of ‘High Penetration Ratio with Reserve’ and ‘Utilizing Product of Wind Speed and Capacity Distributing Frequency-regulation Task’ is proposed to enhance the economics and rationality for unit dispatching and task distribution of wind farm.Based on MATLAB/Simulink platform,the improved 3-machine-9-bus system is simulated and analyzed.The integrated frequency regulation control strategy is verified in large-scale wind farms with invariable wind penetration ratio of 40%.The strategy can deploy wind turbines at full wind speed to ensure the economic and stable operation for power system,which is scientific and effective.