| Distribution network is an important part of power system.As the most direct link connecting power users,low-voltage distribution network has a direct impact on the operating state and economic benefits of power system.In China,the geographical distribution of low-voltage users is relatively dispersed,and the distribution platform is still used as the power supply unit.Distribution transformers,lines,users and distribution devices,as components of the station area,are the key to the intelligent development of low-voltage distribution network.Therefore,it will be the development trend of energy conservation in the future how to consider the economic benefits of the station from the planning and operation cycle of the power equipment,and reduce the power loss,construction and maintenance costs.At the same time,the battery energy storage is developing vigorously and is widely used in the planning and operation stage of the power system.This paper focuses on the planning model of the low-voltage distribution network framework and takes the low-voltage distribution network as the research object to study the application of the energy storage battery system in the low-voltage distribution network.The main work is as follows:(1)Focus on the problems of too large transformer capacity and unbalanced low-voltage line load,a low-voltage grid planning model is proposed including partition of the transformer supply zones and generation of the low-voltage network topology considering complementary of DGs and loads.The low-voltage grid planning problem is decoupled into the planning of distribution transformers and the low-voltage networks.In the distribution transformer partition model,we consider the constraints of power supply distance and the transformer capacity,as well as the DG-load output complementarity.In the low-voltage network planning model,a heuristic topology programming algorithm is designed with considering of the indexes of DG-load balance,load balance and line distance balance.The optimization target is to minimize the annual cost of the system.Application test shows that the proposed scheme can well balance the DG and load among transformers and low-voltage feeders and effectively reduced the overall annual cost of the system.(2)Focus on the problem of special transformer capacity planning caused by rapid load growth,an optimal energy storage strategy is proposed to reduce transformer capacity.Firstly,the load model considering daily and monthly characteristics is established,and a comprehensive revenue model is established by energy storage cost,the benefits of reducing special transformer capacity planning,participating in the electricity energy market and government subsidies.Calculate the cost and benefit of energy storage operation based on long time scale.And the problem is solved by the CPLEX solver.In the numerical example,the comprehensive benefits of energy storage under users with different characteristics are analyzed,and the user characteristics suitable for energy storage configuration are pointed out.This part also studies and analyzes the energy storage benefits with the impact of energy storage cost changes and government subsidies changes,which provides beneficial references for the application of energy storage in user side scenarios.(3)Considering the problem of transformer and line overloading,the energy storage sitting and sizing model suitable for the low-voltage grid side to alleviate the upgrade of power equipment is proposed.Firstly,the comprehensive value evaluation model of grid side energy storage is constructed.Secondly,a two-layer optimization model combining the sitting and sizing problem of energy storage is constructed.The upper layer optimizes the capacity and power of energy storage connected to the low-voltage network,while the lower layer optimizes the energy storage location and installation number of energy storage.A hybrid differential evolution algorithm with two layers of alternating iteration embedded in power flow calculation is used to solve the sitting and sizing model.Finally,the change of each index before and after energy storage configuration is analyzed.The calculation example shows that the reasonable sitting and sizing of energy storage can effectively avoid the overload problem of power equipment.The economic benefits of energy storage can be improved and the comprehensive benefits of energy storage can be improved by comprehensively considering the benefits of transformer loss reduction and network loss reduction. |
