Research On Optimization Strategy For Network Reconfiguration And Island Partitioning Of Faulted Distribution Network Containing Distributed Generation

In the distribution network system,the distributed generation(DGs)penetration rate is increasing day by day.Using DGs supplies short-term power in the distribution network,constructs intentional islands,and makes uninterrupted power supply for critical loads,which is of great significance for improving the reliability of distribution network.And at the same time,it also provides a new choice for traditional fault recovery methods of distribution network.However,after a large number of DGs are connected to the distribution network,the network changes from a single power supply to a multi-point power supply system.And it makes the network structure more complicated.There are many options for failure recovery method of distribution network.The main work of thesis is divided into the following aspects:(1)Establishing a model for service restoration of distribution network ensures to supply the reliability of critical load power and maximize the load recovery.It is suitable for multiple faults of multiple DGs.In order to realize the two methods of network matching between network reconstruction and islanding,a fault topology identification method based on the parent-child list is proposed.Based on the simplified graph,the depth-first search method is used to form the parent-child list,which quickly identifies the fault topology and matches the corresponding recovery method to improve the recovery efficiency.(2)DGs are widely used in distribution networks due to their non-polluting and safety reliability.Considering the randomness of wind power and photovoltaic power generation,the mathematical fitting models of power distribution are given respectively.Based on the system network loss and line load balance,the optimization target the dual-objective reconfiguration model of distribution network is established.Rapidity is one of the basic properties of self-healing of smart distribution network.For the typical invalid solution generation of complex ring networks,this paper gives four coding rules not to eliminate invalid solutions in network reconfiguration.At the same time,it makes all the solutions feasible in the reconfiguration process to achieve fast network reconfiguration.Finally,the improved firefly algorithm is used to iteratively solve the reconfiguration model.The case study shows that in the case of DGs,it is verified that using fast distribution network optimization reconfiguration strategy can greatly balance and improve many basic indicators of the network.(3)A multi-objective reconfiguration model based on game theory is proposed,which takes into account the randomness of wind and photovoltaic power output.And it aims at reducing active power loss,balancing load overload and minimizing switching times.Taking the three objective functions as different players and considering the constraints among the objectives,a cooperative game alliance model is constructed to explore the possible relationships among the objectives.Finally,the improved firefly algorithm is used to solve the game reconfiguration model iteratively.And the final reconfiguration results are determined by ranking the fitness values.The example shows that improved firefly algorithm can quickly solve the multi-objective reconfiguration game model to obtain its equilibrium solution;the number of scenes has certain influence on the reconfiguration optimization index;the number of scenes is negatively correlated with the network loss and running time,and the load balance degree is positively correlated and has no obvious relationship with node voltage.(4)In order to solve the problem of fast service restoration in distribution network with distributed generations(DGs),a multi-stage service restoration method is proposed.The service restoration method organically combines the four phases of service topological identification,islanding,connectivity restoration with main network of DGs and network reconfiguration,and load shedding operation.Once the distribution network is faulty,the service area is identified by the service topology identification method to determine the next stage of service restoration execution and to update the topology parameters.During the island configuration phase,the islanding method based on depth-first search algorithm is proposed.Its goal is to restore the key load,maximize load recovery,and improve the utilization of DGs.Optimizing the tie switch quickly by heuristic rules restores the out-of-service areas and the main network connectivity.Network reconfiguration phase based on the parent-child list rules avoids infeasible solution.And the flow calculation is used to verify whether the next phase is executed or not.The load shedding stage removes the non-critical load to ensure the stable work of the system.The example shows that this method is suitable for the case of large-scale out-of-service,multiple failures,and cascading failures in the distribution network with DGs.It can make an effective restoration strategy according to the actual situation and improve the efficiency of complex fault restoration with strong applicability.