Research On Reliability Assessment And Service Restoration Of Active Distribution Network

With the advantages of environment friendly and flexibility,the distributed generations(DGs)have been highly valued and widely promoted in many countries.The large number of DGs accessing changes the topology structure,operation mode and power supply reliability.Active distribution networks(ADN)can effectively solve the problems caused by DGs.Compared with traditional distribution network,the reliability assessment model and method have changed greatly.Component failure is the main factor affecting the power supply reliability.Aimed at the component failure,the service restoration of distribution network is mainly to restore the power supply in the non-fault power loss area by changing the state of the branch switch,which is an important means to improve the reliability of power supply.Therefore,this paper studies the reliability assessment and service restoration of ADN.The main research work is as follows.Firstly,power flow calculation is the precondition of distribution network operation analysis.This paper summarizes the power flow calculation model of DG,and calculates the power flow by the backward/forward sweep algorithm,and analyzes the influence of DG on node voltage and network loss,which prepares for the studies of distribution network service restoration.Secondly,network topology analysis is the basis of distribution network reliability assessment.This paper encodes the topology of power distribution system based on the method of feeder division to improve the efficiency of reliability analysis.The two-state Outage model of components is established to simulate the state changing process of components.Taking into account the random factors such as wind speed and illumination,time series output models of wind turbine and PV array are established.Considering the limitation of the charging and discharging power of the energy storage device,the total capacity of the energy storage and the external factors,a charge-discharge model of energy storage is established.Considering the load fluctuation over time,the time series model of load is established,which lays a theoretical foundation for the subsequent reliability analysis.Based on the feeder division and DG output model,this paper adopts the failure mode effect analysis method to divide the fault area,puts forward the DG using strategy in island area.Considering the timing output of wind turbine,PV and energy storage and the demand of load,the load reduction strategy is formulated.On this basis,the reliability assessment procedure based on sequential Monte Carlo simulation is given.This paper analyzes the reliability of the modified IEEE RBTS BUS6 test system containing DGs and studies the impact of DG's accessing type,accessing capacity and accessing location on the reliability,which verifies the correctness and validity of the reliability assessment method in this paper.Finally,in order to improve power supply reliability,aiming at the fault condition of components,a method of service restoration of ADN with DG islanding and out-island reconstruction is proposed.In the aspect of islanding,considering the important load level,the power flow restriction,the islanding partition model is established,and the breadth-first search algorithm is used to solve the islanding area.For the area outside the island,a reconfiguration model considering active loss and the number of switching operations is established.The improved binary particle swarm optimization algorithm is used to solve the reconfiguration scheme.The two improvements are as follows:the loop-based coding method can effectively avoid infeasible solutions,and adopting the decreasing linear inertia weight and asynchronous changing learning factor help to improve the learning ability and adaptability of the algorithm.Finally,the IEEE33 node system is taken as an example to study the service restoration of single fault point and double fault point,which verifies the effectiveness of the proposed method.