Research On SVG For Three-phase Four-wire Power System

With the progress of society and the continuous development of power system,a large number of non-linear power equipment appear in the low-voltage distribution network system,resulting in a large number of reactive power consumption and three-phase imbalance problems,seriously affecting the reliable operation of distribution network,reactive power balance and power quality.Static Var Generator,as a flexible dynamic compensation device,can solve the problem of unbalanced three-phase system on the one hand,and track and compensate the reactive power of the system on the other hand.It has become an indispensable equipment in power system to improve power quality.In this paper,the static var generator(SVG)used in low-voltage distribution network system is studied.Firstly,the working principle and topology of SVG are introduced,and its mathematical model is constructed.Then the reactive current detection algorithm based on instantaneous reactive power theory is analyzed and compared,and the appropriate reactive current detection method is selected.At the same time,the control strategy of SVG is selected according to the characteristics of low-voltage distribution network.Finally,a load simulation model with harmonics,zero-sequence current and three-phase unbalance is established based on MATLAB/Simulink platform.The simulation results show that the proposed method has good control effect on low-voltage three-phase four-wire distribution network.The specific work of this paper is as follows:(1)The basic working principle and compensation principle of SVG are introduced.Then,the SVG model based on reactive power compensation of low-voltage three-phase four-wire distribution network is established.(2)Aiming at the special load of low-voltage distribution network,several reactive current detection methods and control strategies of SVG are studied,and the improved dq0 current detection method based on instantaneous reactive power theory and hysteresis comparison control strategy are selected as the current tracking control method of SVG.(3)On the basis of theoretical research,the SVG simulation model is built by using MATLAB software,and the simulation analysis is carried out under the three-phase unbalance and three-phase equilibrium respectively.The simulation results show that the SVG can solve the problem of unbalanced current compensation when the three-phase unbalance occurs in the power grid system,and also can compensate reactive power very well.The feasibility of the detection and control method is verified.