The Research On Voltage Sag

Voltage sag is one of the most important electromagnetic interference (EMI) that modern electric customer must be faced. Sensitive loads can't run properly because of the sag of power system. The sag proved to be costly to industries, so it's important to reseach and prevent the sensitive loads from voltage sag. This paper will discuss the voltage sag in four aspects, including the measurement and evaluation, analysis and computation of the sag, research on the sag detection and DVR(Dynamical Voltage Restorer).In the introduction of the sag, we introduce the sag definition and discuss the sag generating resourecs and the interference description. The paper bats around the sag measuerment and evaluation from the mechanmism, character, statistics rule, danger to the sensitive loads and impossible solution. The paper analyzes the voltage sag and its propagation path from the point of view of electric circuit. In the rule of the sag, Dynamic Voltage Restorer (DVR) is considered as the most effective device to compensate the voltage sag. As it is important to detct the sag in the real time, this paper proposes a new voltage sag detection method based on an improved synchronous reference frame transform which can use two sampling points to abstract the fundamental RMS and phase without the necessity for locking vlotage phase, but the low-pass filter influence the detection precision. The paper designs the main circuit of the 380V, 20kVA DVR. The filter and control scheme design is according to the proposed circuit and the simulation experiment is done. The result indicates the DVR can compensate the voltage sag quickly with high precision.