Analysis And Research On Early Warning Of Three Phase Unbalance In Smart Grid

In recent years,due to the ever-increasing living standards of the people and the large-scale use of high-power household appliances,The phenomenon of the three-phase unbanlanced in the low-voltage network area has become more and more serious.Therefore,the goal of domestic and foreign experts and scholars is discovering the three-phase unbalanced phenomenon in the power system timely.As one of the main standards of power quality,our country and foreigner have given a variety of definitions of three-phase unbalance degree.These calculation methods mainly divided into the sequence component method based on phase sequence decomposition and the approximate method using effective value calculation.This article mainly uses PS CAD simulation software to simulate and analyze the existing main three-phase unbalance calculation methods,analyze their advantages and disadvantages,and point out the non-uniqueness and limitations of the sequence component method and inaccuracy and limitations of the approximate algorithm.Next,The article improves the definition of three-phase unbalance degree.I use the ratio of the sum of squares of the measured values of the three-phase negative sequence component and zero sequence component to the square of the three-phase positive sequence component to define the three-phase unbalance degree.Next,I use the vector decomposition method to derive,and use the measured value of the three-phase vector to express the definition of the three-phase unbalance degree.Such it can avoid the complicated vector calculation of the sequence component method.Finally,In order to verify its effectiveness,I use PSCAD software to simulation the three-phase unbalanced power system.The new definition of the three-phase unbalance degree unifies the non-uniqueness problem between the negative sequence unbalance degree and the zero sequence unbalance degree that both based on the sequence component.On the other hand,this method uses the effective value of the three-phase vector to calculate,so its calculation is simple.Therefore,this method has a good application prospect,which the low-voltage network area that use three-phase four-wire power system exist zero sequence component of my country.