Research On Service Restoration For Distribution System With Soft Open Point

Extreme events may damage the connection path between the transmission grid and the power distribution system,which cause large-scale blackouts in the distribution network,major economic losses and adverse social impacts.At this time,local distributed resources such as distributed generations(DGs)and energy storage systems in the distribution system can be used to quickly restore critical loads,which is conducive to reducing power outage losses and enhancing the resilience of the distribution system against extreme events.Soft open points(SOPs),as a new reactive power adjustment device,can improve adjusting the power flow and implement optimization operation thus enhance operation performance of distribution systems,and improve the restoration ability for resilience enhancement.Therefore,the main research contents of this paper are as follows:First,to tackle critical loads restoration problem for active distribution system with multiple SOPs under blackouts after extreme events,this paper proposes a two-step load restoration method.Firstly,a mixed-integer second-order cone program(MISOCP)is solved for determining the restoration strategy of each period.Secondly,determine the action sequence and the control mode of SOPs between periods by the proposed restoration action rules.The MISOCP model maximizes the weighted cumulated service time for critical loads,subject to operation constraints on the network,power sources,and the SOPs.According to the results by the first step and the function of SOP in the system,the restoration operation rules determine the switch sequence and SOP control modes,aiming at restoring critical loads as soon as possible.The analysis of the case verifies the effectiveness and superiority of the proposed method.Then,in order to change the distribution system from fault state to restoration state quickly and smoothly,it is necessary to optimize the switching operation sequence.This paper proposes a restoration operation sequence decision-making method for smart distribution systems considering multiple sources coordination.The problem is modeled as a mixed-integer linear program which can be solved by the optimization solver to determine the optimal switching operation sequence and system operating status after each operation.The objective is to serve more critical loads as fast as possible.The unbalanced three-phase power flow constraints,operation constraints and switch operation constraints are considered.Case study verifies the effectiveness of the proposed method.Finally,the inertia of an isolated system formed by inverter-based DGs is relatively low,so the dynamic frequency during the restoration is essential as it may trigger the protection and cause restoration failure.This paper proposes a dynamic frequency constrained service restoration method for the distribution system.First,according to the frequency response of inverter-based DGs,the analytical formulation of the system frequency nadir is derived and piecewise linearized.By incorporating the linear frequency constraints,a mixed-integer linear program is proposed for the restoration problem,by solving which the optimal switching sequence and the system operation state after each restorative action can be determined.The effectiveness of the proposed decision-making method of restoration sequence for the distribution system considering dynamic frequency constraints is verified through the analysis of the case and the simulation.