Influence Analysis Of Wind Power Inertia Control On Power System Stability And Research On Frequency Regulation Optimization Strategy

With the increasing penetration of non-synchronous generator power sources represented by renewable energy such as wind power,the dominant position of synchronous generator power sources in the power system will be broken,and the operation characteristics of the power system will change fundamentally.Inertia control technology is a solution to the problem of equivalent inertia reduction caused by wind power integration.By simulating the inertia response and power frequency droop characteristics of synchronous generators,the frequency stability of power system is improved.Nevertheless,it will also cause the electromechanical scale coupling between the non-synchronous generator power sources and the synchronous generator power sources in the system,superimposed on the uncertainty of wind power output,which leads to the difficulty in power system stability analysis and control system design.Therefore,revealing the influence mechanism of wind turbine inertia control on the stability of power system has important theoretical value and engineering significance.Meanwhile,in the face of complex and changeable operating conditions,how to make use of the advantages of flexible and controllable inertia of wind power,rationally configure the inertia control parameters to meet different control objectives,optimize the performance of frequency regulation controller,improve the frequency response characteristics of the system are also the problems that need to be solved urgently in the current wind power inertia control technology research.In this dissertation,doubly-fed induction generators(DFIGs),which is the mainstream application of wind farm,is taken as the research object,and the synthetic inertia(SI)control technology is selected as the realization route of wind power participating in frequency regulation,and the following research work is carried out:(1)The dynamic interaction model between the DFIG subsystem with additional SI control and the single machine infinite bus subsystem is established.The block diagram of Phillips-Heffron model is drawn.The influence path and mechanism of SI control of wind turbine on power system stability are analyzed by using damping torque analysis method.Meanwhile,based on the relationship between wind turbine access point frequency and power system frequency,a linear small signal model is established to further analysis the influence trend of SI control parameters of wind turbine on damping ratio and oscillation frequency of the system.It is pointed out that different SI control parameters and wind power penetration rate will affect the system oscillation mode and the damping torque provided by the wind turbine to the system electromechanical oscillation loop,and unreasonable parameter configuration will even lead to negative damping torque.Moreover,the dynamic characteristics of wind turbine are coupled with system dynamics,and the effect of the control parameters on the system oscillation mode is affected by the inertia and damping level of the system.(2)Based on the virtual inertia of power system,the concept of virtual damping is proposed,and the significance of virtual damping to improve system stability is pointed out.The mathematical relationship between the SI differential control parameter and virtual inertia,as well as the SI droop control parameter and virtual damping is derived.Meanwhile,in view of the coordination problem between the additional SI control parameters,a novel control strategy combining the online identification of the dominant oscillation mode of the system and the particle swarm optimization(PSO)is proposed.By making full use of the virtual inertia and virtual damping,the stability of the power system under high wind power penetration is further improved,and the multi-objective comprehensive optimization of frequency stability and power angle stability under multi-operation scenarios of the power system is achieved.(3)The grid-connected wind turbines with controllable inertia introduce new inertia and damping characteristics to the power system.This new characteristic is affected by the inertia control parameters of wind turbine and coupled with the original inertia and damping characteristics of the system,which increases the complexity of system stability control.To solve this problem,based on the power balance principle,the equivalent rotor motion model of the synchronous generator considering the influence of the SI control is established,and the control influence and fault factors are uniformly expressed as the parameter perturbation of the equivalent inertia and bounded uncertain disturbance.Then,by using the sliding mode variable structure method,combined with the variability and controllability of the equivalent inertia and equivalent damping,an adaptive robust-sliding mode control(AR-SMC)strategy is proposed to improve the power system stability.The theoretical derivation and simulation analysis show that compared with the traditional inertia control method,AR-SMC control strategy can better reduce the frequency change rate,suppress the relative power angle oscillation amplitude and improve the system stability.(4)The SI variable parameter method for wind turbines can better take into account the system frequency response characteristics and rotor operation safety under different wind velocities.However,the dynamic change of control parameters will also change the system state during operation,thus affecting the performance of AGC controller designed based on specific system operating points.To solve this problem,this dissertation proposes an AGC inter-source coordinated control strategy considering the influence of wind farm additional SI variable parameter control.At the wind turbine level,the SI variable parameter control based on load shedding reserve state is realized.Meanwhile,the system state change caused by parameter switching of this control strategy is included in the parameter design of AGC controller,which realizes the following of system state change and improves the frequency response characteristics.At the level of inter source coordination,the wind farm is included in the frequency regulation dispatching system of the power system,and the power distribution coefficient is dynamically adjusted according to the wind velocity and the reserve capacity of wind power frequency regulation,so that the wind farm can participate in the secondary frequency regulation of the power system within the available power range to ensure the continuous grid-connected operation of the wind farm.