Research On Coordinated Control Method Of Inertia And Primary Frequency Regulation For Doubly-Fed Induction Generator Based Wind Turbine And Station Energy Storage

The large-scale grid connection of wind power not only alleviates the pressure of environmental pollution and resource shortage,but also promotes China’s energy develop in the direction of low-carbon,clean and sustainable.However,as permeability of wind power continues to increase,the security problems faced by power grid are also emerging.As one of the mainstream models,doubly-fed induction generator based wind turbine(DFIG-WT)usually operates in the maximum power tracking state without reserve active power.Therefore,it does not have the dynamic frequency response capability in face of frequency fluctuation,which will lead to the reduction of equivalent system inertia and primary frequency regulation capability,and bring hidden danger to the safe and stable of power grid.In order to solve this problem,the frequency regulation potential of rotor kinetic energy and installation topology of station energy storage are studied in this paper.By coordinated controlling rotor kinetic energy and supercapacitor,the frequency regulation problem caused by wind power grid connection can be effectively solved.Firstly,the mathematical modeling of DFIG-WT’s each part is performed in twophase rotating coordinate system,and control block diagram of DFIG-WT’s control system are also introduced.Then the station energy storage equipment,supercapacitor,which is applied in coordinated control of wind/storage for frequency regulation,is determined.And its classical mathematical model is also established.Secondly,a virtual inertia general control strategy considering continuous frequency fluctuation is proposed,which is used to solve the inadaptability of traditional virtual inertia control scheme when applied in transmission line short-circuit fault.By introducing the maximum positive frequency deviation and the logic judgment link of short-circuit fault occurrence and cutting,it can adjust the control parameters of the virtual inertia accordingly and realize the control strategy converse with different frequency response events automatically.By introducing the maximum negative frequency deviation,it can keep DFIG-WT provide constant additional power at the point of lowest frequency,ensuring that rotor speed decelerate to a stable operating point after releasing the kinetic energy.Simultaneously,by setting the logic judgment link of frequency,it can control rotor speed rise again after system frequency returning to the rated value and avoid the phenomenon of frequency secondary drop.Then,the power support capability of DFIG-WT’s rotor kinetic energy is quantified,and feasible region of DFIG-WT participating in frequency regulation is determined.On these basis,a inertia and primary frequency regulation control strategy based on rotor kinetic energy and supercapacitor energy storage is proposed.When load increases,DFIG-WT releases rotor kinetic energy to provide inertia support and supercapacitor outputs active power to participate in the primary frequency regulation.When load decreases,frequency regulation is provided by DFIG-WT itself.And for the problem of power sudden drop and power loss happened at rotor kinetic energy exiting inertia support under the condition of load increase,supercapacitor and the change of power-rotor speed tracking curve are used to solve it.Finally,the four energy storage frequency regulation schemes under combination of coordinated control strategy of wind-energy storage,frequency regulation strategy based on supercapacitor,centralized and distributed energy storage are introduced.Theirs energy storage capacity,service life,economic cost and technical performance are also compared and analyzed.And the most advantageous configuration scheme is determined,which is the coordinated control strategy of wind-energy storage under distributed energy storage.