Operational Flexibility Enhancement with Aggregated Electric Vehicles based on Virtual Energy Storage Model

Distribution network (DN) operational flexibility refers to the adaptability of DNs to uncertainties in sources and loads, which is directly related to the reliability and economics of power supply. With the large-scale integration of distributed energy resources (DERs) into DNs, higher requirements are placed on the operational flexibility. As an important load component in DNs, the optimal control of electric vehicles (EVs) is the crucial mean to improve operational flexibility. However, optimizing the charging and discharging power of a large number of EVs requires a significant amount of computation time, making real-time control of EVs difficult. Therefore, this paper aggregates a large number of EVs based on a virtual energy storage model (VESM), and proposes an optimization method for the VESM to obtain its controllable power and capacity limits. In order to reduce computation time, an online tracking method of the controllable power and capacity without re-solving the optimization model is proposed. Finally, the effectiveness of the VESM and proposed online tracking method are verified in both residential and workplace area by case studies.