Research On Active Frequency Support Optimal Control Technology Of Large-scale Wind Power

Wind power is developing rapidly in China,the installation and energy production have ranked first around the world.Compared with synchronous generator such as hydro and thermal power,wind power has weak inertia and weak frequency support capability,and does not respond to and support grid frequency variations actively.As a result,when conventional generators are largely replaced by wind power,system inertia response(IR)and primary frequency regulation(PFR)capabilities will continue to decline,and frequency stability problems are becoming prominent increasingly,which leads to many frequency stability incidents all over the world.The system frequency stability has become a key technical bottleneck restricting the safety and stability of the system,as well as the healthy development of wind power.At present,some research has been carried out globally on the wind power active frequency support(AFS)technology,and the active power-frequency supplementary control has become the mainstream way to realize the wind power AFS.However,unlike conventional generators,the aerodynamical-mechanical-electrical multi-physical and control links of wind turbines are interactively coupled in a wide frequency band,and the supplementary control will have an impact on the stability and dynamic characteristics of both wind turbines and power grid frequency,where the mechanism of action and the rule of change are not fully clear yet.Furthermore,the wind power generation is fluctuating,and the number of wind turbines in the wind farm is large,whose operating conditions are highly diverse and variable.Therefore,it is very difficult to realize the highperformance and high-reliable AFS control.Given the above needs and problems,this paper mainly investigates the theory and optimal control of large-scale wind power AFS technology,the topic has important theoretical significance and engineering application value.The main research and innovation of this paper are summarized as follows:1)The state-space model of the wind power grid connection system including active frequency support control is established,and the influence of AFS control on dynamic characteristics of wind turbine and power grid frequency is analyzed.Specifically,the state-space model of the grid connected double fed induction generator based wind turbine(DFIG-WT)system including AFS control is set up.Based on the eigenvalue analysis,the influence of each physical and control link of the wind turbine on the oscillation mode is studied,and the influence and change rule of AFS control on the stability and dynamic performance of wind turbines are clarified.On this basis,the system load frequency response model is introduced,and the transfer function between wind power AFS control and system frequency is described.Based on the frequency domain analysis,the effect of AFS control on system frequency stability and dynamic characteristics is studied,and the selection principle of frequency active support control parameters for system stability is specified.2)The optimal control methods of wind turbine adaptive virtual inertia and coordinated primary frequency regulation are proposed,which improve the inertia response and primary frequency regulation performances of wind turbines.The inertial response capability,influencing factors,and the change law of aerodynamicalelectrical energy of wind turbines are analyzed,and the technical characteristics of AFS based on rotor kinetic energy,rotational speed reserve,and pitch angle reserve are compared and studied.Regarding the two mainstream operating conditions of power reserved and maximum power point tracking(MPPT),a coordinated and optimal control strategy for PFR is proposed based on multi-energy coordination,which improves the response speed and stability of PFR for power reserved wind turbines.Also,a fuzzy adaptive virtual inertia control(VIC)method of wind turbines operating on MPPT state is proposed,which improves the frequency response characteristics of the system and avoids the problem of secondary drop.3)The optimal primary frequency regulation control methods wind farm based on distributed autonomy and centralized coordination are proposed,which improve the primary frequency regulation performance of the wind farm and ensure the safety of the mechanical load of wind turbines.The active power-frequency control topology and AFS control of wind farms are studied,and the AFS of wind farms is summarized as a multi-constraint multi-objective optimization problem.Considering the different status of wind power in system frequency regulation sources,a distributed and autonomous model predictive control(DAMPC)method based on wind turbine health state is proposed for wind farms PFR.The proposed method realizes the self-adaptive optimal distribution of the frequency regulation power according to the health status of wind turbines,which is conducive to reducing the failure rate of wind turbine.Besides,a centralized and coordinated model predictive contro(CCMPC)method is proposed for wind farm PFR considering the fatigue load of wind turbines,which realizes the dynamic autonomous response of wind power to the grid frequency variation process and the active optimization of additional mechanical loads from PFR.The proposed method reduces the fatigue load of wind turbines while improving the system frequency response.4)Hardware-in-the-loop simulations and field tests of wind farm active frequency support.The wind power multi-controller hardware-in-the-loop(HIL)experiment platform is set up,and the wind power PFR HIL experiments and analyses are carried out.Furthermore,based on large disturbance filed test of the power system,the wind farm AFS performance is analyzed in the grid-source coordination demonstration of China Northeast Power Grid,and the feasibility and effectiveness of the wind farms participating in the grid IR and PFR are verified.The wind power AFS optimal control methods proposed in this paper have all been validated by time-domain simulations.And the traditional PFR method of wind farm undering different operation conditions has been verified by HIL experiments,and further applied to the grid-source coordination demonstration wind farms in China Northeast Power Grid.The wind power AFS performance has been verified by system-level large disturbance tests.The results of this paper provide a scientific basis and reference for the engineering application of large-scale wind power AFS technology,which is conducive to the safety and stability of highly penetrated wind power systems,as well as the healthy development of the wind power industry.