Research On Meticulous Voltage Control Strategy Of SVG And Wind Farms Connected To The Grid

GREEN AND SUSTAINABLE has become the theme of today’s energy construction and development.With the rapid increase in the scale of new energy grid connection,the problems related to the voltage stability of the power system that follow have become more and more significant.The voltage qualification rate of the high-proportion of new energy areas is always low.In order to increase the regional reactive power reserve,Static Var Generator(SVG)is currently used as the reactive power compensation device of wind farms.However,due to the failure to coordinate the control of the SVG and wind farms,SVG often assumes a larger amount.The amount of reactive power compensation is not conducive to the stability of the system voltage and the service life of the equipment.Furthermore,new energy-intensive areas are often connected to the grid through a common line,and the distances between the new energy areas are often relatively short.The control strategy can be used to realize the reactive power allocation between the areas.Thereby,meticulous control of voltage under large-scale new energy grid connection is realized.In order to give full play to the reactive power compensation capability of the doubly-fed wind farm,this paper firstly analyzes the reactive power adjustment mechanism and reactive power limit of Doubly-Fed Induction Generator(DFIG)in detail.By calculating the capacity and overcurrent on the stator-rotor side and Grid-side Converter(GSC)side.The relationship between DFIG reactive power limit and electromagnetic power P_e and slip s is visually presented in a three-dimensional view.On this basis,based on the DFIG in MPPT mode,the current DFIG traditional reactive power control structure is improved,the variable coefficient droop control is introduced,the DFIG terminal voltage is adjusted according to the reactive power limit change,and the output reactive power is distributed to the stator-rotor side and GSC side.In addition,the function of wind curtailment and load reduction is added to further improve the reactive power compensation capability of DFIG under extreme conditions.The effectiveness of the improved DFIG reactive power control structure is verified by a wind farm grid-connected model composed of three DFIG units.This paper improves the SVG reactive power loop to increase its sensitivity to the grid-connected node voltage,and adds advanced control,so that SVG can better cope with sudden changes in voltage.On this basis,combined with the improved DFIG unit,a coordinated control strategy with SVG fast response as the mainstay and DFIG reactive power support as the auxiliary is designed to realize the meticulous regulation and control of the grid-connected node voltage.The advantage of coordinated control strategy compared with traditional control is verified through the SVG cooperative wind farm grid-connected model.In this paper,by analyzing the main situation of regional voltage compensation,using improved SVG,DFIG units and coordinated control strategies,a regional reactive power allocation strategy is designed.This strategy can detect the grid-connected bus voltage and the combined bus voltage in each area,and select the area that can participate in the reactive power compensation according to a calculation method of the reactive power evaluation coefficient Mi provided in this paper.On this basis,the M_i calculation type Particle Swarm Optimization(PSO)makes the reactive power compensation between areas more reasonable.By building a two-region grid-connected model,the feasibility of the strategy is verified,and the traditional sensitivity-based PSO algorithm is compared to verify the effectiveness of the M_icomputational PSO algorithm in this paper.