Type And Capacity Planning Of Distribution Transformer Considering The Impact Of Distributed Photovoltaic And Energy Storage Access

Distribution transformer(DT)is an important power equipment in the distribution network.It is of great value in energy conservation and loss reduction because of some characteristics,such as long running time and wide distribution in the distribution network.How to make an economic and scientific investment decision is an important issue for designing a safe,reliable and economical distribution network.Distributed generation(DG)is clean,efficient and can be flexibly controlled.photovoltaic(PV)is a kind of DG,and has attracted much attention since its low cost and convenient installation.In recent years,a large number of PVs have connected to low-voltage girds,and their output increases the risk of overload of DT because of its fluctuation and randomness.As a controllable DG,energy storage could balance the load of DT by power control,and further have an influence on the decision of DT capacity.In this paper,the DT economic benefit considering distributed PV and energy storage is evaluated,and the main contents are as follows.A model considering the load and PV uncertainty is proposed,and a timing evaluation index of DT based on voltage,load rate and operation cost is put forward.Simulation and calculation are made under the conditions of different load type,weather,PV penetration rate,DT type and DT capacity.And,the influence on selection of DT type and capacity is studied when the PV is connected to low voltage distribution system.Then,considering physics,operation,economic life of DT,a variable life model is built.For the impact of PV on life of DT,a life cycle cost(LCC)model based on variable life is raised,whose validity is verified by simulation and calculation.According to the aforementioned life model and taking energy storage control into account,a new bi-level planning method considering energy storage and PV is proposed.In the aspect of model,the upper model aims at minimizing the LCC of the DT,and determines the type and capacity.Considering the influence of the uncertainty of PV and load,setting the opportunity constraint on the state variables,the lower model determines the variable life of the DT and the timing of charge and discharge control of the energy storage under each operating year,which is based on the changing characteristics of each sub-item of the distribution LCC with different operating years,and sets the minimum variance or square sum of the equivalent injected active power at the low-voltage side of the DT as the target.In the aspect of algorithm,a cataclysmic genetic algorithm is used so solve the upper problem;GAMS solver CONOPT and point estimate method are jointly used to solve the lower problem.Simulated and calculated results prove the effectiveness of the method.At last,this paper selects two types of DT as representatives,and summarizes the recommended table of DT average capacity per household under different load types,average installed capacity per household of PV and average optical storage allocation ratio.