Power Transfer Optimization Of Distribution Networks In Consideration Of Loop Closing Current Constraints And Multi-Voltage-Level Coordination

Load transfer without power cut will become an important tend of future distribution system in load balancing,but the loop network operation may generate a high circulating current,causing the relay protection devices to maloperation,which will lead to failure of power transfer and the larger range of blackout.After distributed generations are connected to the distribution network,the active output adjustment of adjustable distributed generations before loop closing can be used to make constraints in the loop closing process satisfied as far as possible.Each voltage level distribution network is connected and restricted,if the overload of a single voltage distribution network is not handled properly,it may be transferred to a higher voltage level distribution network,and cause greater risk of blackout and higher cost of transfer.Thus,this paper studies the power transfer optimization of distribution networks with adjustable distributed generations in consideration of loop closing current constraints and coordinated power transfer optimization of multi-voltage distribution network.The main contents of this paper are as follows:(1)The loop closing process lacks effective control means,and the potential of distributed generation to alleviate load overload and increase loop closing freedom has not been fully tapped.For the problem that loop closing transfer for 10 k V distribution network with adjustable distributed generations,a power transfer optimization model of distribution networks with adjustable distributed generations in consideration of loop closing current constraints is proposed.This paper analyzes and obtains the loop closing steady state and transient current constraints of the feeders with DGs.Then,a power transfer optimization model is proposed in the constraints of distribution network power balance,radial grid structure and substation transfer capacity limitation,for the objective function of minimum switching number.Afterwards,a verification of loop closing current constrains and optimal regulation of DGs’ outputs model is established in the constraints of loop closing steady state and transient current constraints,for the objective function of minimum DGs’ outputs change.And the above models are integrated to form a loop closing transfer optimization model of distribution network.(2)The overload of the distribution network can be solved through the transfer assistance of the upper or lower power grid.For transmission congestion and overload of equipments during peak load period,a coordinated power transfer optimization model of multi-voltage distribution network is established.This paper first analyzes the typical structure of high and middle voltage distribution network,then establishes wiring topology and derives the active power balance equations of various typical topologies.Making full use of the network characteristics of distribution networks at all levels,combining active power balance,substation output,line ampacity,and topology constraints.A coordinated power transfer optimization model of multi-voltage distribution network considering topology constraints is proposed for the objective function of minimum switching cost in power transfer operation.(3)In order to verify the correctness and effectiveness of the models and methods proposed in this paper,simulation models of actual 10 k V single-stage and110 k V/35 k V/10 k V multi-stage distribution networks are built in MATLAB respectively.Firstly,aiming at the overload problem of 10 k V distribution network,the simulation results between without considering and considering distributed generations output active regulation are compared.The results show that the proposed model can effectively solve the problem of unbalanced load in distribution network.Then,according to the common transfer demand of the multi-level distribution network,without considering and considering the difference of transfer cost are simulated and analyzed respectively.The results show that the proposed method can realize coordinated power transfer of multi-level distribution network under lower cost and operational risk.