Model Of Smart Distribution System Security Region Based On AC Power Flow Calculation

The existing models of Distribution System Security Region(DSSR)are based on DC power flow,which does not take the network loss and voltage drop constraints into account accurately.In order to solve this problem,this paper models the DSSR based on AC power flow and the model improves the calculation accuracy of the DSSR.First,this paper introduces the power distribution system N-1 security.According to the real situation of power grid and the model character,it gives the N-1 calibration based on AC power flow calculation.Through comparison with the conventional N-1 calibration based on DC power flow,the advantages of the N-1 calibration considering AC power flow are analyzed.The processes of two kinds of the N-1 calibration are compared and summarized.Secondly,this paper simplifies the existing model of Total Supply Capability based on AC power flow.The mathematical general formula of the DSSR based on AC power flow is given,which considered network loss and voltage drop constraints.The DSSR mathematic model based on AC power flow is established.It solves the high precision demand of the calculation problem of DSSR boundary in the secure situation.Finally,this paper observes the security boundary of distribution system by AC power flow simulation method.It analyzes the error between the boundary of DSSR based on AC power flow and existing the boundary of DSSR based on DC power flow.Combined with the results of N-1 calibration,it researches the error of these two kinds of the boundary of DSSR.The effects of network loss and voltage drop constraints on accuracy of the model is analyzed by an example,it is found that the two-dimensional section of DSSR decreases with the increase of network loss and the lower limit of voltage constraint,however,the shapes of them are similar.The applicable scenes of the different models of DSSR are obtained,and the selection suggestions for the models of DSSR are given: when the voltage constraint is strict,it is recommended to use the model of DSSR based on AC power flow;when the voltage constraint is wide,if the length of line is shorter,it is suitable to adopt the model of DSSR based on DC power flow;if the length of line is longer,it is suitable to adopt the model of DSSR based on AC power flow.In addition,the security region model which considered distributed energy storage is researched by the existing model of DSSR based on DC power flow which is considered DG.The effect of energy storage on load and DG is analyzed by an example,the effects of energy storage access on the security boundary of DSSR are analyzed from the three different aspects: area change,shape characteristics and quadrant characteristics.It provides a theoretical basis for modeling the DSSR based on DC power flow which considered DG and energy storage.