## 1 Introduction  
Recently, energy shortage and atmospheric pollution problems are becoming critical issues, as high energy consumption and carbon emissions are caused by traditional combustion engine vehicles. As an effective way to solve these problems, electric vehicles (EVs) have become an essential component in the transportation sector to reduce dependence on oil resources and improve environmental performance with various types of renewable energy resources in the microgrid (MG). In addition, plug-in electric vehicles (PEVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell vehicles (FCVs) are not only cost-effective but also eco-friendly in terms of energy prices and operating expenses compared to combustion engine vehicles [1]. As EV infrastructure rapidly grows, EVs provide the function of stabilizing the power system. For technological advances in power management of EV infrastructure, an EV aggregator is utilized to offer energy-efficientand cost-effective charging/discharging strategies. With batteries equipped in EVs, they can operate as an energy storage system (ESS) shifting load demand from peak to peak-off hours and reducing electricity costs [2]. A three-step approach is proposed to manage PHEVs' charging load to minimize the cost for energy suppliers [3]. Moreover, EVs are described as controllable loads which can be utilized to stabilize the grid supporting the energy in vehicle-to-building (V2B) or vehicle-to-home (V2H) applications, and can also serve as spinning reserves in specific conditions [4; 5; 6]. With the widespread usage of EVs, the structure of the parking station is presented to satisfy the electrical energy requirements of EV owners. These requirements of parking stations are satisfied by interacting with the utility grid. The parking station satisfies the accessibility to the charging station for EVs and provides an opportunity to integrate the EVs' batteries. Moreover, when vehicle-to-grid (V2G) or grid-to-vehicle (G2V) technologies are used for EVs, batteries of EVs at parking stations can serve as a flexible reserve capacity [7]. Due to their ability to store energy, parking stations can participate in the energy and reserve markets. In addition, parking stations can perform a prominent role to supply charging services for EV owners. Generally, conventional EV chargers, such as AC Level 2 (charging rate is 10-22 kW) and direct current quick charging (DCQC) (charging rate is 50-120 kW), are used in public charging stations [8]. As various types of chargers have different charging rates and characteristics, different charging modes can be assigned to EVs depending on the EV charging requirement. As more chargers are installed in a charging station, more installation and operating costs are incurred. Consequently, it is significant to use a limited number of chargers efficiently. Several studies were presented to satisfy multiple EVs' charging requirements, such as the development of intelligent charging strategies [9; 10], and optimization of charging stations' location and size [11; 12]. Cooperative charging strategies will lead to an increase in operational efficiency and the reduction in electricity costs. EV charging stations generally produce high charging load in the distribution network when added to the local power systems. Several studies have been implemented, which are relevant to quantifying the variation of peak load [13; 14]. With an uncoordinated charging scheme for PHEVs located in the metropolitan distribution network of Australia, peak load shifting was required to make the stable operation of the distribution network [15]. In [16], the impact of uncontrolled EV charging on local power distribution networks was analyzed, and the distribution networks were stabilized by incorporating a coordinated charging scheme. Moreover, the optimal strategy, which controls the charging activities in the parking station, was presented by analyzing the effect of EV charging on daily load demand [17].