The Research Of The Governance For Voltage Sag Based On Dynamic Voltage Restorer

With the rapid advances of science and technology and the growing development ofindustrial scale, kinds of sensitive and sophisticated electrical equipments are widelyapplied to all areas of the society. The equipments can’t work well thanks to the problemsof power quality, so as to significant economic losses. Therefore, it’s necessary to takeeffective measures to improve the power quality for social progress. The fault of voltagesag is the most common among the problems of power quality. Dynamic voltage restorer(DVR) which is the most effective tools to solve the problem of voltage sag can takeaction in a few milliseconds. It can rapidly eliminate the fault of voltage sag. It canimprove the power quality to ensure reliable operation of the load. As with good dynamicperformance and high cost, dynamic voltage restorer has become the most effective andeconomical electrical installation.This paper mainly discusses the working principle and topology of dynamic voltagerestorer in detail. Detection method, compensation strategy and control scheme for DVRare studied in depth. The detection method with instantaneous reactive power theory andits improved scheme can detect the magnitude and phase of voltage sag accurately andquickly. The establishment of the simulation model verifies that the method can meet thetesting requirements. The mode of constant power and the mode of constant voltage andconstant frequency are proposed in the article. The simulation models of inverter arecreated by using sinusoidal pulse with modulation (SPWM). In the end, the simulationresults output the stable sine wave voltage. So it can guarantee reliable voltagecompensation of dynamic voltage restorer.Three basic compensation strategies which are in-phase compensation, pre-sagcompensation and minimum-power compensation are proposed based on the voltage,current and power of DVR. It finally gets the specific relationship between the power ofDVR and factor of load that the low power factor of the load can reduce the output powerof DVR by researching the minimum-power compensation in different scope ofcompensation. Therefore, the structure of the compensation system can be improved byusing parallel reactors with switching device in the terminal load. When the system is compensated by DVR, we can reduce the power factor temporarily to ensure effectivecompensation of DVR. Finally, it is verified that controlling the power factor through theshunt reactor can reduce the power injection, enlarge the voltage sag range of purereactive compensation and mitigate the severer sag with longer duration by the simulation.