Research On Power Electronic Balancing Device In Power System

Electric energy is the most important energy source in modern human society,and it plays a vital role in the normal operation of human society.Therefore,ensuring the safe,stable and efficient output of electric energy is a very important research direction.And the electric energy itself takes a kind of commodity,its commodity quality regulation is also an important subject.An important standard to ensure power quality is to ensure that the threephase power network operates under the condition of balance.However,in modern power grid,with the rapid development of industrialization and civil use,power electronic equipment has been widely used.This will make the power grid operate under the condition of three-phase imbalance in most cases,which will cause harm not only to the client,but also to the transmission end and the power grid system itself.To avoid this kind of damage,the hazardous parts of the grid should be analyzed first.By analyzing the three-phase power grid,we can decompose the three-phase power into positive sequence component,negative sequence component and zero sequence component.When the three-phase power grid is in normal operation,the negative sequence component and zero sequence component in the grid are all zero.When the power network operates under the condition of asymmetry,there will be negative sequence and zero sequence components in the power network.Negative sequence component will cause motor and transformer heat.So the negative sequence component of compensation network becomes the main research direction of this paper.After consulting relevant literature,it is found that the research and compensation of negative sequence component is a separate research direction,namely,reactive power compensation.Static reactive power generator(SVG)is the most widely used reactive power compensation device.At present,the research of reactive power compensation is mainly divided into two parts,that is,the reactive current is extracted first,and then the appropriate device is controlled for reactive power compensation.This paper also carries on the research according to these two parts.First,the research history of reactive current extraction is studied.After analyzing the theory of reactive power and instantaneous reactive power,it is found that although this method has been widely used at present,phase-shifting operator is used in the calculation process,and the method has its own delay.Therefore,an improved instantaneous symmetric component method is proposed in this paper.By constructing a delay-free rotation vector,the instantaneous values of positive and negative sequence components of three-phase current can be obtained in real time.Because there is no need to calculate the trigonometric function,the calculation process of this method is simple.Based on this method,a new positive and negative sequence current detection method,namely the generalized DQ transformation method,is proposed on the basis of the commonly used DQ transformation method.This method does not need to use the phase-locked loop,which changes the traditional DQ transformation method which uses the phase advance data to calculate,and uses the real-time current and voltage data to calculate.The method of reactive current detection is simulated and verified in MATLAB/Simulink.The experimental results show that the new method is more responsive than the traditional method.At present,the main SVG control mode is PI control,but due to tuning parameters,PI control has some defects.According to the compensation principle of SVG,a double closedloop control system with outer voltage loop and inner current loop is designed.Since the main research content of this paper is the direction of reactive power compensation,it only needs to ensure the stability of the voltage loop,so the traditional PI controller is used for the voltage loop.The current loop is controlled by feedforward decoupling.In order to ensure that the system has strong robustness and anti-interference function,the sliding mode control is adopted in the current loop,because of its sliding mode characteristics,it can have better anti-interference characteristics.In addition,due to the defects of sliding mode control itself,there will be the defect of oscillation in the control,so the super helical second order sliding mode control which can resist oscillation is adopted.After the drive signal is generated by feedforward decoupling control,the drive signal is acted on the SVG bridge circuit by SVPWM modulation.Based on this method,a static reactive generator model is designed in Matlab,and the dynamic three-phase unbalanced load is simulated and analyzed.The simulation results show that compared with the traditional PI control,this method has better control effect.