Research On Voltage Sag Control Of Distribution Network Based On Dynamic Voltage Restorer

With the continuous development of power technology,a large number of power electronic equipment with high demand for power quality are applied to production and life,the whole power grid structure becomes increasingly complex,so the transient power quality problem is more and more concerned by people.according to the relevant research data,it is proved that voltage sag are the most likely and most serious transient power quality problems.among them,dynamic voltage restorer is recognized as one of the most effective ways to solve the voltage sag problem.at present,the analysis and research of DVR mainly focus on the following aspects: first,what kind of topology is adopted by the main circuit;second,whether the voltage drop can be detected quickly and accurately;third,what kind of compensation strategy and control strategy are adopted by DVR.In this paper,the working principle of DVR is described,and the system structure of DVR in distribution network is analyzed in detail.The large capacity energy storage capacitor is used as the DC energy storage element,and the cascaded multilevel inverter is used as the core power unit of DVR.The SPWM modulation method based on carrier phase-shift is chosen as the modulation law of inverter.The advantages and disadvantages of dq detection method based on the traditional instantaneous reactive power are discussed.The dq transformation method and dq derivative transformation method are analyzed in detail.This idea will be used to construct a virtual coordinate system for derivation in the αβ transformation detection method,and the simulation results show that the derivation method has better real-time performance and stability.In addition,aiming at the problem that DVR device can not take into account both the system stability and the dynamic response speed,an improved PR compound control strategy is adopted,which makes DVR device can further improve the harmonic characteristics of the system voltage while compensating the load voltage.In the compensation strategy,the minimum energy compensation method is used.Finally,the simulation model is built in Matlab / Simulink software to carry out simple voltage sag detection and compensation control strategy simulation verification.From the simulation results,it can be seen that the DVR device designed can realize the compensation of voltage sag in distribution network,reduce the loss of active power,and effectively extend the compensation time.