Research And Design Of Three-phase Static Reactive Power Generator In Low Voltage Distribution Network

Nowadays,various kinds of non-linear devices in low-voltage distribution network will consume a lot of reactive power,and inadequate reactive power capacity or excess capacity in the network will have a serious impact on power quality.Therefore,fast and effective reactive power compensation is of great significance to improve the reliability of power supply.Static Var Generator(SVG),as an advanced dynamic reactive power compensation device,has the advantages of fast response,less harmonics,small volume and low operation and maintenance cost.However,the traditional control strategy of SVG has the problems of low robustness and high coupling,which make the control of SVG more difficult.Based on the analysis of the traditional control system and control theory of SVG,the control strategy is improved to make the SVG control system have higher robustness and lower coupling.Firstly,the necessity of studying the SVG control system is analyzed,and the working principle of the SVG device is elaborated in detail.According to the input and output characteristics of the system,the mathematical model of the SVG device in operation state is established,and the good stability of the mathematical model in normal operation range is verified.On the basis of comparing and analyzing the p-q detection method and i_p-i_q detection method based on three-phase instantaneous reactive power theory,a new double closed-loop control strategy based on direct current control is proposed.The sliding mode variable structure control method is used to control the external loop voltage on the DC side instead of the traditional PI control method,so that the voltage stability of the DC side of the system is better and the convergence speed is faster.Decoupling control is adopted to reduce the coupling of the system and optimize the control effect.On this basis,the hardware circuits of SVG including the main circuit,driving circuit,auxiliary power supply circuit,Signal Detection Circuit and main controller are designed,and the software flow charts of the control system including the main program flow,double closed-loop control flow,interrupt protection flow,SVPWM modulation flow and digital filter flow are further designed.Finally,the control system of SVG is simulated and validated by matlab/simulink under three conditions:load capacitance,load induction and load nature changing from capacitance to induction.The simulation results show that the SVG control system designed in this paper can realize fast,dynamic and stable compensation for reactive power.