Research On Fault Restoration Control Method Of Distribution Network Considering Loop-closing Voltage Impact

With the growing energy crisis and environmental pollution problems,the penetration rate of distributed generation(DG)such as wind power and photovoltaic increases year by year,and the traditional distribution network gradually transforms to active distribution network.The load transfer process of distribution network fault restoration depends on the operation of loop-closing and loop-opening.The loop-closing process is prone to nodal voltage impacts,and the randomness and complex response characteristics of DG power output may make the voltage impacts increasingly severe,yet the existing studies do not focus on the problem of voltage impacts resulted from loopclosing process.On the other hand,regulating DG power can suppress voltage impacts to a certain extent,but the power control capability of DG has obvious dynamic characteristics and also triggers dynamic changes in grid control demand.Now,there is a lack of coordination between the adjustment of DG output and the action of the switch,which will affect the fault restoration efficiency,leading to the inability to effectively suppress voltage impacts.In addition,under different switching schemes,the different control volume of DG for suppressing voltage impacts,resulting from loop-closing process,leads to the different suppression effect of voltage impacts,so it is necessary to match switch operation and DG power control in time sequence.However,most of the existing optimization methods focus on the overall load transfer scheme,and seldom take into the impact of the loop-closing voltage,which will affect the reliability of the load transfer scheme.Therefore,this paper investigates the principle of active adjustment of DG power considering the safety of loop-closing voltage impact,further considers the correlation between DG power control and switching action,and proposes a fault restoration control method of distribution network considering the suppression of loopclosing voltage impact to fully ensure the reliable implementation of the load transfer scheme.The main contents are as follows:First,the control structure components of three types of DGs,including variablespeed wind turbine,photovoltaic,and energy storage systems,are analyzed,the influence of the control characteristics of DGs on their power control in fault restoration scenarios is considered,and the active power control capability and reactive power controllable range of each DG are modeled.Through electromagnetic transient simulation of the distribution network containing DGs,the operational characteristics of DGs during fault restoration are analyzed,followed by the controllability of DGs in the loop-closing process of the distribution network.Then,an active adjustment method of DG power capable of efficiently suppressing voltage impact to a safe range is proposed for the problem that the control demand of voltage impact in the load transfer process is not matched with the control capability of DG.The power of the distribution network in the loop-closing process is analyzed,based on which the generation mechanism and influencing factors of voltage impacts at nodes in the loop-closing process are analyzed,and the control demand of voltage impacts in the loop-closing process is quantified.Based on the relationship between voltage control demand and DG power in the loop-closing process,the DG power demand for suppressing loop voltage impacts is derived,and combined with the analysis of DG power control capacity,the DG control volume calculation method considering of loop-closing voltage impacts are proposed,which maximally suppresses the loop-closing voltage impact during the load transfer process in distribution network fault restoration,and effectively improves the safety and reliability of the new energy power system.Finally,a fault restoration control method of distribution network considering the suppression of loop-closing voltage impact is proposed for the problem that it is difficult to effectively suppress the voltage impact due to the uncoordinated DG output adjustment and switching action during the fault restoration process.The correlation between the two means of DG output adjustment and switching action is analyzed from the perspectives of rate of load restoration and voltage impact during load transfer.The fault recovery problem is divided into the master problem of fault restoration optimization and the subproblem of fault restoration control sequence optimization.The solution of the master problem is taken as an argument to the subproblem.In the sub-problem,a control sequence combination with "DG power control-closing branch switch-opening branch switch-DG power reset" as the basic steps is formed.In each basic step,the DG power reference value is determined by the proposed active adjustment method of DG power that considers the suppression of the loop-closing voltage impacts,and then the feasible control sequence combination with the smallest deviation from the solution of the master problem is obtained,which ensure the reliable implementation of load transfer methods to the greatest extent.