Research On The SVG Of Three-phase Four-bridge Arm For Three-phase Unbalanced Treatment Of Low-voltage Distribution Network

Three-phase four-wire system is mainly used in China’s low-voltage distribution network.Due to the increasing loads,three-phase imbalance has become one of the most important problems in low-voltage distribution network.In this paper,three-phase four-leg SVG is used to solve the three-phase imbalance problem of low-voltage distribution network,which improves the system control strategy and power quality,and has significant theoretical significance and engineering practical value.Firstly,this paper introduces the background and significance of the topic selection,the development status and development trend at home and abroad.Because there is zero sequence current in the neutral line of three-phase four-wire system,this paper adopts four-leg SVG device to control the three-phase imbalance,and analyzes the current compensation methods and current tracking control strategies commonly used in traditional SVG.Secondly,the three-level four-leg topology is introduced,the traditional algorithm is improved,and an improved symmetrical component detection method is proposed,which simplifies the calculation process of matrix transformation and reduces the calculation error.The three-level four-leg 3D-SVPWM modulation strategy is optimized,which does not need coordinate transformation and simplifies the calculation process.In order to ensure the tracking effect of command current,a quasi-PR controller is adopted.The SVG simulation model is built in Simulink environment.The simulation results show that the three-level four-leg SVG system designed in this paper can quickly compensate the imbalance of load current under different load switching conditions,and has a good compensation effect,which verifies its effectiveness and practicability.Finally,the overall structure of the main circuit of the three-level four-leg SVG system is designed,including the design of the control circuit part and the software program logic part of the control system,and an experimental platform is built to verify the compensation effect of the SVG system on the three-phase imbalance.