Active Distribution Network Expansion Planning

The traditional distribution network planning takes much bigger capacity margin to achieve the feasible solution which can cover the operation problems during the planning stage.The method of the traditional distribution network planning is simple and the assets in the distribution network cannot be fully utilized.The traditional distribution network planning cannot coordinate the controllable equipments in the planning stage,including the distributed generation(DG),the flexible network topology structure and the flexible load;also cannot exert the system support function from the DG nor decrease the investment cost of the planning scheme.In order to plan the distribution network reasonably and elaborately,the active management schemes of the controllable equipments in the distribution network should be considered in the planning stage,including the DG,the flexible network topology structure and the flexible load,etc.In this dissertation,the different active management schemes of active distribution network(ADN)are analysed.Then the distribution network expansion planning models which adapt to different needs and purposes of planning are proposed.The main conclusions in this dissertation are as follows:(1)The mechanism of the different active management schemes is analysed based on the voltage increasing characteristics at DG connecting point.The Second-Order Cone Programming(SOCP)model of DG accommodation is proposed with the power flow of distribution network and constraint relaxation.The active management schemes including the DG dispatch,On-Load Tap Changer(OLTC)adjustment,reactive power compensation,are considered in the model.(2)The power flow model of distribution network suitable for the ADN expansion planning is proposed.Based on the newly proposed power flow model,the ADN expansion planning model considering the uncertainties of DG and intermittent energy is proposed.The objective is to minimize the comprehensive expense of total social costs of the distribution network in the planning period.The DG dispatch,OLTC adjustment,reactive power compensation,Demand Side Management(DSM)are considered.The constraints consist of equipment construction and installation constraint,the network operation security constraint and active management constraint.The transformer loading rate constraint and the OLTC adjusting frequency constraint are considered.The planning model can adapt to the uncertainty environment and practical distribution network management in the future.The scenario analysis method is utilized to decrease the complexy of the model solving,then the proposed model is transferred to SOCP model to find the optimal solution.(3)The method of the distribution network expansion planning considering distribution network reconfiguration is proposed;the distribution network reconfiguration is taken as the expansion planning alternative with zero investment cost of the branches;during the process of the reconfiguration in expansion planning,all the branches are taken as the alternative branches.The ADN expansion planning model considering the distribution network reconfiguration is proposed based on the SOCP model of distribution network reconfiguration.Besides of the traditional active management constraints,the distribution network reconfiguration is included.(4)The Battery Energy Storage System(BESS)operation model considering the cycle life is proposed based on the BESS operation characteristic.The ADN expansion planning model integrating BESS is proposed;the objective is to minimize the comprehensive expense of total social costs of the distribution network in the planning period,which includes the benefit from peak shaving because of the BESS installation.The BESS optimal operation is considered as one of the active management constraints.(5)The SOCP model of ADN multistage expansion planning is proposed.The branch,DG and substation installation constraints between different planning stages are considered,which can assure the reasonable linking between the planning schemes of different stages.The proposed model can assure that the planning schemes of different stages can fulfill the load increases.Analysis on a typical Portugal 54-bus system and a practical East China 73-bus system,as well as the comparison between the planning results with and without considering active managements,prove the feasibility,validity and applicability of this dissertation.