Research On Primary Frequency Regulation Control Strategy Of DFIGs In High Wind Power Penetration Power System

In order to alleviate the shortage of fossil energy and protect the ecological environment,renewable energy,represented by wind power,has developed rapidly.Wind power penetration in power system has steadily increased.Large-scale wind power integration brings clean and renewable energy,but also brings great challenges to the safe and stable operation of power system,especially in the aspect of system frequency.The mainstream wind turbines represented by doubly fed induction generator(DFIG)are integrated to power system through power electronic interface.System inertia and frequency regulation capability are reduced since the decoupling of DFIG's rotor speed and system frequency.In order to ensure safety and stability of power system frequency,the participation of DFIG in primary frequency regulation(PFR)of power system becomes a necessary condition for its grid-connected operation.Therefore,it is of great significance to research on PFR control strategy of DFIGs,which can make DFIGs provide better PFR service.This paper establishes a model of DFIG participating in PFR control of power system.Based on the model,a coordinated control method of DFIG participating in PFR control at any given wind speed is proposed.The practical modification of this coordination method is carried out to make it suitable for all-wind conditions.Finally,the PFR capability of DFIG with coordinated control is evaluated.The specific contents include:(1)DFIG participating in PFR control model of power system is established.The essence of DFIGs participating in PFR is expounded,that is,DFIG responds to system frequency and actively changes electrical power to support system frequency.By regulating mechanical power,electrical power is balanced in order to maintain the safety and stability of rotor speed.Based on this,the power regulation method of DFIG is analyzed,and the realization of DFIG power reserve is studied.On the basis of theoretical analysis,power regulation and power reserve are realized through several sub-modules,thus the PFR model of DFIGs is built.(2)In view of the indeterminacy coordination of DFIG PFR methods and insufficient consideration of rotor kinetic energy,a coordinated control method of DFIG PFR method with given wind speed is proposed.Essentially,the coordination of various PFR methods is the regulation of control parameters of different methods.The problem of DFIG PFR coordinated control is transformed into a single objective multi-parameter optimization problem.In the optimization problem,there are a large amount of calculation,and electromechanical transient simulation is introduced.Moreover,the relationship between control objectives and control variables cannot be expressed analytically.Above all,particle swarm optimization(PSO)algorithm is selected after comprehensive comparison of several optimization algorithms.The original PSO algorithm is improved by Latin hypercube sampling,dynamically regulated hyper parameters,mutation operation and parallel computing.The improved PSO algorithm is used to solve the coordinated PFR control model of DFIG at a given wind speed.At the same time,the optimal control parameters under the wind speed are obtained.(3)To overcome the shortcomings of the coordinated PFR control method of wind turbines with given wind speed,the practical modification is carried out to obtain the coordinated PFR control method of DFIG with full wind speed.At the cost of reducing PFR effect with partial wind speed,the suitable range under a set of PFR control parameters can be extended.The theoretical optimum with each wind speed is transformed into the sub-optimal control with multi-wind speed.The practical modification of coordinated PFR control method is transformed into the problem of wind speed discretization.The conventional discretization method is not suitable for problem of wind speed discretization.On the basis of supervised merging discretization,a discretization method based on evaluation index of PFR accuracy loss is proposed.In order to adapt to the characteristic of wind speed fluctuation,the discretization results are modified to have hysteresis characteristics.(4)To clarify PFR capability of DFIGs with different wind speeds,a method for evaluating the PFR capability of DFIG in power grid is proposed.Effect of steady-state PFR is focused on in the method,and DFIG equivalent droop coefficient is used to describe the capability of DFIG participating in frequency regulation.Based on linearization of wind power coefficient and dynamic analysis of electrical power and pitch angle,the equivalent droop coefficient formula of DFIG is derived.Starting from the calculation formula,the key factors affecting the frequency regulation ability of DFIG are analyzed.The validity of the proposed PFR capability evaluation method is verified by Shandong power grid model simulation.