Research On The Control Strategy Of HVDC-Thermal Power-Wind Power Joint Regulation For Large Capacity DC Transmission Grid

The penetration rate of new energy in the power system is increasing year by year,and the large-capacity DC external transmission grid concentrates on absorbing the surplus power of new energy,providing a guarantee for emergency power support between regional grids.However,as a high proportion of power electronic equipment is put into operation,the equivalent inertia of the system is greatly reduced,and the frequency robustness is seriously threatened.For this reason,the virtual synchronization technology is applied to power electronic equipment such as new energy and DC,which effectively improves the equivalent inertia of the system and helps to stabilize the system frequency dynamically.This paper establishes an equivalent model based on the wind-heat bundled DC external power grid in the Northwest region and the large-capacity AC/DC hybrid power grid in the Northeast region to study the DC-thermal power-wind power joint frequency adjustment strategy under high-penetration new energy.The specific research content is as follows:First of all,a wind-fire joint control strategy is proposed for the characteristics of high wind power penetration rate and low overall inertia of the Northwest Power Grid.Establish thermal power unit model,HVDC power transmission model,static reactive power compensation model,virtual inertia control model of doubly-fed wind turbine.Propose virtual inertia loop adjustment coefficients,droop loop adjustment coefficients,and weight coefficients that characterize the relative short-circuit capacity of grid nodes;define the virtual inertia adjustment degree,calculate the electromagnetic compensation power provided by the virtual inertia control of the wind turbine at different time scales,and coordinate the participation of thermal power units primary frequency modulation.Secondly,a direct-fire joint control strategy is proposed in view of the low wind power penetration rate of the Northeast Power Grid and large-capacity DC transmission.Based on the actual grid structure in Northeast China,the equivalent model of the AC/DC hybrid system is built,and the frequency auxiliary control system of the HVDC system is designed.Propose a method to modify the parameters of the DC auxiliary frequency modulation controller;study the influence of the controller parameter changes on the system frequency stability;define the frequency modulation participation degree of the DC controller,and quantify the additional trigger angle of the HVDC system.Third,for the wind power system to sacrifice the rotor kinetic energy to participate in the kinetic energy recovery process after the primary frequency modulation,the second frequency modulation method of the wind field under steady frequency is formulated.Propose the delay switching function of the virtual inertial control system,combined with the weight coefficients to make the wind farm hierarchically and hierarchically exit the virtual inertial control when the system frequency is restored to the steady state;propose a scaling factor to solve the problem of sudden changes in the q-axis component of the control system during the restoration of the rotor kinetic energy.Finally,with two characteristic power grid structures as the research background,the direct-fire-wind joint regulation control strategy of large-capacity DC external transmission power grid is formulated.Establish a coordinated dynamic power adjustment system for thermal power units,wind power units,and DC systems;analyze the influence of multiple operating conditions on the frequency stability of the frequency modulation system.The frequency modulation control method proposed in this paper can effectively improve the equivalent inertia of the system and the dynamic frequency adjustment ability,so that the frequency modulation process of wind turbines and DC transmission systems has temporal and spatial distribution characteristics,and the rotor kinetic energy recovery time is shortened to less than 3 s,which is for the subsequent multi-energy grid connection The frequency optimization strategy of the flexible AC/DC hybrid system has laid the theoretical foundation.