Optimal Control Technology Of Primary Frequency Regulation In Power Grid With Wind-storage Combined Operation

With the national "30.60" dual carbon goal,new energy power generation represented by wind power continues to develop rapidly.At present,wind power generation systems are all operating in the maximum power mode,aiming at the maximum efficiency of wind energy,and cannot provide additional inertia and backup frequency regulation capacity when the frequency of the power system changes.With the continuous increase of the penetration rate of wind power generation,the capacity and output of conventional units in the power grid are greatly compressed,resulting in insufficient frequency regulation capacity and inertia of the power system,which is not conducive to the stable operation of the power system.For wind turbines,the ability of independent frequency regulation is limited,and it is easy to waste wind resources,and frequent adjustments of the speed will reduce the operating life of the unit.Energy storage has precise,fast and flexible power response capabilities and can participate in power system frequency regulation.However,due to the high investment and operating costs of energy storage,the feasibility of participating in frequency regulation alone is restricted to a certain extent.Therefore,how to build the wind storage joint frequency modulation system so that it can not only give full play to the respective frequency modulation characteristics of wind farms and energy storage but also improve the safe and efficient operation level of energy storage has become a research hotspot and core key problem to be solved urgently.This paper has done the following work:(1)The structure,working principle,and mathematical model of the DFIG and the energy storage system are analyzed,and the control method of the DFIG and the energy storage system are described in detail.(2)The mathematical equation of the primary frequency regulation of the power system is established,and the influence of wind power grid connection on the inertia and frequency regulation capacity of the power system is analyzed.And the virtual inertia control,pitch angle control,and over-speed control of wind turbines,as well as droop control and virtual synchronous control of energy storage,are analyzed.An adaptive frequency modulation control method for energy storage based on the virtual synchronous inertia coefficient is proposed.Based on the above research,a wind-storage combined frequency regulation system is constructed.The wind turbine over-speed control and the energy storage virtual synchronous inertia adaptive control is selected as the wind-storage combined frequency regulation control strategy.A simulation platform is established to verify the effectiveness of the wind turbine,energy storage,and wind-storage combined frequency regulation control strategies.(3)A combined wind-storage integrated frequency regulation control strategy considering wind-storage combined hierarchical regulation and energy storage operation interval optimization is proposed.Among them,the wind farm and its supporting energy storage system are regarded as the frequency response control object of the power grid,and the layered control is adopted,and the virtual synchronous inertia adaptive control is used as the upper control of the entire wind-storage combined system.A power optimal allocation method is proposed to determine the respective power response targets of the wind farm and energy storage and then complete the respective frequency regulation power responses;At the same time,the principle of energy storage operation interval optimization is proposed.According to the state of charge(SOC)of energy storage,the operation interval is divided into the normal frequency regulation area,early warning area,and forbidden area to improve the safe and efficient operation level of the energy storage system.Through simulation analysis and verification,the wind storage integrated frequency modulation control strategy of wind storage combined layered regulation and energy storage operation interval optimization can not only effectively participate in the power grid frequency modulation response,but also realize the reasonable distribution of frequency modulation power between the wind farm and the energy storage system,taking into account the efficient utilization of wind energy,the effectiveness of wind storage combined frequency modulation and the safety level of the energy storage system.