Energy Storage Allocation Considering Vulnerability Of Active Distribution Network

Vulnerability of power grid directly reflects structure robustness and power supply capability of power grid.The structure and state of active distribution network are faced with greater uncertainty.Therefore,it is urgent to propose reasonable vulnerability assessment indicators according to the characteristics of active distribution network,in order to identify and improve key vulnerable components.The energy storage device can support the vulnerable components of the power grid and improve the ability of the distribution network to absorb intermittent DG.In this thesis,the vulnerability of active distribution network is taken into account in the location and capacity of energy storage.The main contents are as follows:(1)The complexity of power grid is discussed,and the network is analyzed according to the complex network theory.Five attack strategies are used to identify the vulnerable components,and three indicators are used to evaluate the network vulnerability: maximum connected area,load loss percentage and transmission efficiency decline ratio.The network topology parameters are calculated by Pajek to analyze the vulnerability of IEEE118 bus system.The simulation results show that: vulnerability increases due to uneven grid structure and it is necessary to identify some key nodes which have great influence on the vulnerability of power grid.(2)Based on complex network theory,the network characteristics of active distribution network are analyzed,and the mathematical models of wind power generation,photovoltaic and energy storage are established.Improved Gini coefficient for node power supply efficiency is proposed to evaluate the uniformity of grid structure,Structural vulnerability index is proposed combining the Gini coefficient and importance of components.Based on the risk theory,a state vulnerability index reflecting the risk of load loss,overload rate and voltage overshoot is proposed.The weight of three risk indexes is determined by EWM.A comprehensive vulnerability assessment system for active distribution network is constructed based on structural and state vulnerability indices,which can be used to assess network vulnerability and identify vulnerable nodes.The rationality of the assessment system is verified by a specific example.(3)The feasibility of applying vulnerability index to energy storage location and capacity is analyzed,and the energy storage allocation method of active distribution network is established: firstly,the vulnerability index of each node is calculated,determining the range of energy storage installation nodes is determined;secondly,the energy storage allocation model is established,and the objective function of the total investment cost of energy storage and operation cost is proposed to minimize the total storage cost,whose constraints include the degree to which energy storage improves vulnerability.The simulation results show that the proposed energy storage configuration method can reduce the vulnerability of the system and total cost In order to improve the bat algorithm for solving the model,an improved bat algorithm based on hybrid adaptive weight and Levy flight strategy is proposed.The algorithm is tested on CEC function set,and the superiority of the improved algorithm is verified by nonparametric test.The simulation of energy storage on the improved IEEE34 bus system proves that the proposed allocation method can improve the vulnerability of the system and reduce the total cost of investment and operation.