Study On Power Grid Frequency Stability Of Doubly-Fed Wind Turbine Participating In System Frequency Modulation

Wind power generation has become the most important part of new energy power generation due to its advantages of no pollution,easy access and low cost.However,the output of wind turbines is closely related to the environment,which cannot be artificially controlled artificially and has strong randomness and volatility.At the same time,large-scale non-inertia wind turbines are incorporated into the power grid,which produces tremendous influence to the frequency stability of the power system.Therefore,this article studies how to improve the traditional double-fed wind turbine to participate in the power grid frequency adjustment to reduce the impact on the power grid and improve the frequency stability of the power grid.To begin with,the operating principle of traditional doubly fed wind turbines was analyzed,and a mathematical model of the main components inside the wind turbine was established in view of its operating principle.The basic principle of the participation of doubly fed wind turbines in frequency regulation was analyzed;At the same time,a mathematical model of the energy storage system was established in view of its operating principle,and the basic principle of the wind storage combined frequency modulation system was analyzed.Secondly,in order to improve the frequency stability of the power grid,the evaluation index for measuring the frequency stability is proposed.This thesis expounds the existing method of variable speed constant frequency double-fed wind turbine to participate in frequency modulation and considers the advantages and disadvantages and applicable conditions of each frequency modulation method,and proposes a comprehensive coordinated control strategy of double-fed wind turbine to participate in system frequency adjustment under full wind speed.This strategy designs and adds a frequency control link to the active power control system in the rotor side converter of the wind turbine and improves the pitch angle control system in the wind turbine hub,let the wind turbine by the rotor kinetic energy conversion of electromagnetic power and load reduction get standby power,and after the active power can active response system frequency changes,output additional active power to participate in the frequency adjustment.The simulation results indicate that compared with traditional inertia control strategies,the comprehensive coordinated control strategy produces more continuous and stable active power output when wind turbines participate in frequency regulation,avoids the occurrence of power pits,and increases the frequency stability of the electrified wire netting.Finally,due to the comprehensive coordination control strategy needs to reserve active power,the active power output in the stable operation of wind turbine is reduced,the utilization rate of wind energy is reduced,and the economic cost of frequency modulation is increased.To solve this problem,it is proposed to integrate the energy storage system into the wind farm and construct a wind farm equipped with energy storage devices.The energy storage devices provide backup power for wind turbines to participate in grid frequency adjustment.By adding Virtual Synchronous Generator control technology to the inverter of the energy storage device,a wind storage virtual synchronous machine model is obtained.By analyzing the frequency modulation strategy of direct suppression of frequency secondary drop through the cooperation of conventional wind storage,it is proposed that the main frequency modulation task is undertaken by the steady-state output of the energy storage system.The wind turbine adopts a wind storage coordinated frequency modulation strategy of comprehensive inertia control assisted frequency modulation,which enables the wind turbine and energy storage system to play their respective output advantages.Through quantitative analysis of simulation results under different conditions,it is concluded that the wind storage coordinated frequency regulation strategy based on steady-state energy storage output can improve the system frequency stability,solve the problem of low wind energy utilization,reduce the configuration capacity of the energy storage system,and improve the economy of frequency regulation.