| The grid integration of large-scale renewable energy generation makes the system highly power electronic,which brings voltage quality problems such as harmonics,voltage deviation and three-phase unbalance.Distributed energy storage system(DESS)has flexible two-way power flow adjustment capability,which can effectively deal with a series of problems caused by the high penetration rate of renewable energy in the distribution network.A reasonable DESS configuration scheme can not only stabilize power fluctuations,reduce network losses,and improve system operation economy.It can also efficiently serve the voltage management of the active distribution network with its flexible operating characteristics,improving the network voltage quality,and enhancing the reliability of power supply.For this reason,based on the 3-phase unbalanced network model,this paper discusses the optimal configuration of DESS in the active distribution network with the aim of improving the voltage quality.The main research contents are as follows:1)The main operating characteristics of the active distribution network are studied,and the3-phase power flow model of the unbalanced distribution network is established;the mathematical models of the inverter distributed power supply and DESS in the active distribution network are analyzed,and the impact on the network after DESS is connected to the grid is discussed.Laying the foundation for follow-up research.2)Aiming at the problem that the traditional DESS optimal configuration research serving active distribution network voltage management usually ignores the 3-phase unbalanced phenomenon of the network,a method for optimal configuration of DESS order in unbalanced distribution network based on voltage sensitivity analysis is proposed.Firstly,the grid-connected position of DESS is determined based on the comprehensive voltage sensitivity analysis;secondly,considering the economy of system operation,the access capacity and operation plan of DESS are optimized with the goal of minimizing the primary energy storage investment and operation and maintenance costs.Finally,the effectiveness of the proposed method is verified by an example analysis.3)Considering that DESS can realize power four-quadrant operation through a power conversion system(PCS),it is easier to control the network power flow.A four-quadrant DESS two-stage optimal configuration method for unbalanced distribution network is proposed.In the stage of site selection,an improved voltage sensitivity analysis method is proposed to determine the grid-connected location of DESS;in the stage of constant capacity,an economic operation model of distribution network is established with the lowest operation cost and the smallest voltage deviation.The example analysis shows that the power four-quadrant DESS can realize efficient voltage regulation through the flexible output of coordinated active power and reactive power,so that the voltage of each node in the unbalanced distribution network is within the specified range while the network operation cost is reduced. |
