Study Of The Control Strategy Of Double-fed Wind Turbines Taking Part In The Primary Frequency Regulation Of The Grid

Wind power generation has been steadily increasing and is predicted to become the primary source of new energy in future power systems.The current main type of wind power generation is the Doubly-fed Induction Generator(DFIG),but its inability to participate in grid frequency regulation caused by rotor-side decoupling limits its effectiveness.With the continued growth of wind power capacity,traditional generating units will decrease and the system will become more volatile and unpredictable,putting pressure on frequency regulation and system stability.Therefore,urgent action is needed to incorporate DFIGs into primary frequency modulation of the system.This paper starts by analyzing the composition of DFIG,analyzing the operating characteristics of DFIG and the principle of vector control power decoupling,building a simulation model and verifying it.Then,the frequency resonance modelling analysis of the classical power system is conducted,and the grid frequency characteristic model is modified corresponding to the decoupling behaviour of the double-fed wind turbine to achieve the frequency characteristic model involving different DFIG permeability.The analysis of the new model shows that the larger the DFIG permeability,the weaker the robustness of the system.The correctness of this deduction is confirmed by the final simulation results.Secondly,a comparison of the characteristics of the DFIG with that of a conventional synchronous generator shows that the DFIG has a strong inertia "hiding" function.because the traditional DFIG uses a fixed coefficient of inertia control and sag control process to engage in the system frequency control can not react to the changing wind speed in time,which may lead to poor frequency regulation effect.The control strategy of variable parameter adjustment is adopted to adapt to the wind speed change and fully exploit the inertial response capability of DFIG;the fan needs to have a certain spare power to participate in the system frequency regulation,and the traditional method of over-speed load shedding cannot adapt to the full wind speed section due to the limitation of fan rotor speed.Therefore,the wind speed is segmented in this paper,and a constant power standby load shedding method is proposed to ensure that the fan has constant standby power in the full wind speed section;by coordinating the control of the two methods in different wind speed sections,a variable parameter adjustment strategy based on constant power standby is proposed to enable the DFIG to adjust its output in response to the change of wind speed.The result of the simulation is that the proposed integrated control strategy can improve the response of the wind turbine to the variation of the wind speed and increase its ability to participate in the frequency control.Then,the problem of restricted fan adjustment range under derated control is addressed After analyzing the characteristics of various energy storage systems,the flywheel energy storage system is chosen to assist in frequency regulation.The system is introduced to address issues such as low power generation efficiency,inadequate speed adjustment,and frequent pitch angle starting under load shedding control.Incorporating the loading and unload of the energy stored system,the fly wheel battery is incorporated into the double-fed system to facilitate system participation.Throughout this process,the control strategy ensures that there is no loss of power generation efficiency and that the flywheel energy storage device maintains virtual inertia control.