Research On Voltage Sag Detection And Location In Power Distribution System With Micro-grid

With the development of a large number of distributed generation in the micro-grid power supply,it have great advantages in reducing the line loss,improving the efficiency of energy utilization,power supply reliability and achieving low-carbon economy.With the DG widely used in micro-grid directly connected to the distribution network,the structure of the distribution network from the radial form of the structure has gradually become a complex network structure of the coexistence of multiple power sources,at the same time the power flow in the distribution network also changes greatly.However,it will pose a serious threat to the stability and security of the distribution network.In addition,the new topology and characteristics of the distribution network also have a great impact on the existing fault location methods,so that the method of determining the location of voltage sag is not accurate or even failure.At present,there are no practical and effective methods to detect the voltage sag characteristic parameters of the DG distribution network and to determine the location of voltage sag.This paper analyzes the influence of a large number of DG access on the distribution network in the micro-grid.With respect to the effects caused by the capacity of the DG,the location of access,the size of the power factor and the characteristics of the DG itself when the DG is connected to the distribution network in the micro-grid,the voltage of each node in the distribution network system is analyzed and simulated in detail.In order to prepare for achieving the location of voltage sag while DG access to the distribution network.Based on the analysis of the method of detecting the voltage sag feature of the Clark-Parker transform,the advantages and disadvantages of each discrete sequence derivation methods are summarized.This paper proposes a method of combining the dynamic prediction algorithm with the differential derivation method could avoid the phenomenon of "burr" caused by the original derivation method in the beginning and ending time of voltage sag,The improved detection method with better dynamic response characteristics can detect the beginning and ending time of voltage sag,amplitude and the change of phase angle immediately and accurately.The method of determining the location of voltage sag by using the set operation and it does well with the case of DG access to distribution network and the operation of the original method is simplified.The simulation results show that the proposed method is effective in the case of fault or missing information.After determining the location of voltage sag,the method based on the voltage sag feature information is used to obtain the distance between the location of voltage sag and the bus,so the detailed location is confirmed.Finally,a numerical example is given to verify the validity of the algorithm through the simulation and analysis.