Optimal Capacity Allocation Of Flexible Multi-state Switch Based On Overload Risk Of Distribution Networks

Flexible multi-state switch(FMSS)is a new type of power electronic device,which is typically used to replace the tie switch in the distribution network.Compared with the traditional mechanical switch,flexible multi-state switch can regulate the power flow at each port in real time and continuously,which can alleviate voltage dip,three-phase load imbalance,balance the distribution of feeder load,improve the permeability of distributed energy,meet the customized power demands of high power quality and high power supply reliability etc.Flexible multi-state switch can actively distribute the load according to the real-time load state of each feeder,fully excavate the power supply capacity of the distribution network,and smooth the load cycle of each feeder,which can not only reduce the operation risk of heavy-load feeder,but also improve the asset utilization and operation economy of light-load feeder,and optimize the operation state of the whole distribution network.In order to quantitatively evaluate the effect of flexible multi-state switch on reducing the overload risk of distribution network,this paper first proposes two simulation methods,which are Monte Carlo method and optimal power flow solving method,and multi-scenario method and optimal power flow solving method.Taking the improved IEEE 33-nodes distribution network as an example,the two simulation methods are compared.The function that flexible multi-state switch can ruduce the overload risk of distribution caused by voltage limit is verified.And this paper analyzes the influence of the capacity change of flexible multi state switch on the overload risk of distribution network.In view of the disadvantage that the simulation method can not guarantee the accuracy of the evaluation results,this paper proposes an analytical calculation method for the overload risk of distribution network with flexible multi-state switch,which is aimed at the distribution network with small circuit parameters and abundant reactive power regulation means.This method ignores the overload caused by the voltage limit,only considers the capacity constraints,and establishes the overload risk of distribution network by load variable space partition method.Analytical expressions of risk index,flexible multi-state switching capacity and load characteristics of feeders are established.Taking the distribution network with three-port flexible multi-state switch as an example,the analytical calculation method of overload risk proposed in this paper is analyzed and verified,and the factors affecting the overload risk of distribution network are analyzed.Finally,based on the analytical method of overload risk assessment of distribution network,the optimal capacity allocation model of flexible multi-state switch is established,which is solved by Newton-Stephenson method.Taking the distribution network with three-port flexible multi-state switch as an example,the optimal capacity allocation of flexible multi-state switch in different operation scenarios is obtained,and the effect of different load characteristics on optimal capacity of flexible multi-state switch are analyzed.