| 30·60 target of Peak carbon dioxide emission and carbon neutrality has already been committed and new type of electrical power system with the renewable energy as the main body has already been proposed in China.In this background,wind energy utilization in the new electrical power system with high-proportioned renewable energy is expanding from local to the whole country.Compared to the traditional thermal power and hydroelectric generators,wind turbines are connected to the power grid through converters and decoupling control of rotor speed and frequency is realized.However,wind turbines lack of inertia and active frequency support capability,great challenges will be introduced to frequency stabilization of new electrical power system with the rapid development of wind power generation.And meanwhile,interaction between machines and power grid of wind turbine is prominent.It also will bring risks to the safety operation of wind turbine machinery under the complex operation condition of power grid.Therefore,this thesis focuses on the frequency stabilization of electrical power system with highproportioned wind energy and the safety operation of wind turbine.Doubly fed induction generator(DFIG)wind turbines as the main object of study,influence of virtual inertia control(VIC)and primary-frequency regulation(PFR)on the wind turbine and grid frequency was researched.Optimal control strategies of VIC and PFR were studied.Active load reduction control strategy of wind turbine under the condition of active frequency support was also studied in this thesis.Research results are benefit to the improvement of frequency stabilization of power system and fatigue life of wind turbines.The main contents and contributions of the thesis include the following aspects:1.The influence of VIC and PFR on the dynamic characteristics of the wind turbine and the system frequency were analyzed.The state-space model of wind turbine with the active frequency support control loops was built.Main frequency range affected by the active frequency support control and their influence on the stability of small disturbance of grid-connected wind turbine system were illuminated.The dynamic frequency response model of the power system with wind power was established.the impact and variation of wind power and its active frequency support control parameters on dynamic charaticristics of system frequency were revealed.It lays foundation for the optimal control of VIC and PFR of the wind turbine.2.The VIC and optimal control methods of wind turbine were studied.The regulation ability of VIC and main influencing factors of large capacity wind turbine were quantitatively analyzed.Then the VIC adaptive control method based on bang-bang and exponential function and the VIC multi-objective optimization control method based on model predictive control(MPC)were proposed respectively,the dynamic response performances of system frequency were improved.Finally,the speed recovery optimization control strategy of VIC was proposed,the secondary drop problem caused by excessive release of rotor kinetic energy was alleviated.The simulation results verified the whole process optimization of the inertia response and generator speed recovery of wind turbine.3.The PFR and optimal control methods of wind turbine were studied.The adapting working conditions and technical characteristics of different PFRs based on rotor kinetic energy,pitch angle reserve,speed reserve and external energy storage of wind turbine were compared and analyzed.The coordinated optimization control was carried out from the point of complementary advantages.The fuzzy adaptive control method of PFR based on the combination of rotor kinetic energy and pitch angle and the piecewise adaptive optimization control method of PFR based on the combination of rotor kinetic energy and DC energy storage were proposed respectively.The response speed and the stability of active power support of PFR were verified by simulation.4.The load response and optimal control method of load reduction under active frequency support conditions were studied.Throughout the research of interaction between power grid and wind turbine,the mathematical relationships of VIC,PFR and generator torque were built.The load response of drive train,blades and tower under different control parameters and strategies of VIC and PFR control were illuminated.Accordingly,an active damping control method of wind turbine drive train under VIC and PFR conditions was proposed.Based on the co-simlation of Bladed and Matlab,the active load reduction effect was verified by the simulation results.5.Controller-hardware-in-the-loop(CHIL)simulation platform of wind turbine was built.VIC and PFR control algorithm were compiled in the physical controller and simulation was carried out.Furthermore,field experiment for the VIC and PFR control of wind turbine was implemented under some typical cases.Throughout the CHIL simulation and field experiment,the feasibility and effectiveness of active frequency support control was verified,which laid the foundation of application for VIC and PFR of wind turbine.This paper focuses on the optimization and improvement of the frequency active support capacity of wind turbines.And it focuses on the rapidity and stability of the frequency active support and the impact on the mechanical loads.Based on the analysis of the influence of the frequency active support on the dynamic characteristics of wind turbines and the frequency of the power grid,a virtual inertia adaptive control strategy,a multi-source reserved primary frequency regulation control strategy and an active damping control method of wind turbine drive train under VIC and PFR conditions were proposed respectively,which improves the performance of the wind turbine’s frequency active support,reduces the mechanical load and fatigue caused by the frequency active support and makes wind turbines more friendly to the power grid,it has certain reference and guiding significance for the development and engineering application of large-scale wind power inertia and primary frequency regulation. |
PDF Full Text Request