Cascaded Multilevel Dynamic Voltage Restorer Detection And Compensation Strategy For Voltage SAG

As the power technology evolving, a large number of power electronic devices whichare required high quality for electricity are applied to industrial production and daily life.So the transmission grid becomes very complex, and transient power quality problems aremore and more attracting attention of people. Data of relevant research prove that, in manykinds of transient power quality problems, voltage sag is the highest probability and themost serious form of harm. Therefore, at this moment scholars from various countries havedone the most extensive and deeply research on the voltage sag. And Dynamic VoltageRestorer (DVR) is recognized as the most effective way to solve voltage sag. Now, analysisand research on the DVR focuses on the following aspects:1) Which topology does themain circuit take?2) The ability to detect the voltage drop quickly and accurately;3)Which compensation strategy and control strategy does the DVR take?In this paper, the above issues are discussed separately. Firstly introduces the workingprinciple of the DVR, the detailed analysis on the various major components include energystorage unit, coupling unit, filter unit and the inverter unit to sum up the cascademultilevel DVR system architecture; Secondly, several traditional voltage sag detectionalgorithms are compared, based on the traditional instantaneous reactive power theory dqtransformation assay, a single phase circuit abc-dq transform voltage detection method isintroduced in detail, the derivation is applied to the dq transformation assay and simulationresults show that the algorithm has better real-time and high accuracy; Finally, severalcommon compensation strategies at this stage are introduced, based on the analysis resultsabout the mathematics model of cascaded multilevel DVR, its compensation strategy andcontrol strategy is studied, the theory suggests that voltage single closed-loop controlstrategy with feed-forward PD control strategy increases the system stability margin, it caneffectively improve the system detects speed and control accuracy. Finally, using MATLAB/SIMULINK simulation software verify that under the control method DVR can achievemore satisfactory compensation effect.