**4. Charging behavior of EVs**

**Figure 2.** Possible contract schemes of EV in EMS: (a) direct contract and (b) aggregator-based contract.

contract scheme.

130 Modeling and Simulation for Electric Vehicle Applications

In a direct contract, the EV owners have the service contract directly with the energy service providers (EMS). In this contract scheme, both the electricity and information are transferred privately and directly between EVs and energy service provider. Therefore, this type of con‐ tract is considered applicable for a relatively small-scale EMS, including BEMS and FEMS, and in where EVs are parked and connected to the chargers for relatively long time, for ex‐ ample during working hours. The main advantage of this type of contract scheme is the abil‐ ity to optimize the profit for the involving entities (EV owners and EMS). Furthermore, controls for both charging and discharging are more simple and faster as EVs are directly and fully under control of EMS. The report in this chapter describes mainly on this type of

On the contrary, in an aggregator-based contract scheme, EV owners have service contracts with the aggregators which are providing and managing electricity services. Therefore, there is no direct contract between EV owners and EMS or other electricity-related entities. The information including EV position (GPS), battery condition (SOC), and estimated arrival time is basically coordinated by aggregator via VIS. Based on these data, the aggregator calculates

Almost all of EVs adopt lithium-ion batteries to store the electricity with consideration of highenergy density, high stability, long lifetime, and relatively lower environmental impact. Charging and discharging behaviors of EVs are influenced by some factors including SOC and temperature [13]. Temperature influences some interface properties of the batteries including viscosity, density, dielectric strength, and ion diffusion capability [17]. Lower temperature results in poor charging and discharging performances because of lower performances of those properties as well as electrolyte limitation [18]. In addition, as temperature decreases, the transfer resistance increases [19].

**Figure 3.** Relationship among charging rate, battery SOC, and charging time during EV charging in different seasons: (a) winter and (b) summer.

Aziz et al. [13] have performed an experimental study confirming the effect of battery SOC and temperature to the charging behavior of EVs in both summer and winter using DC ultrafast charger (maximum charging rate of 50 kW). **Figure 3** shows their experimental results, i.e., the relationship among the charging rate, battery SOC, and charging time. Generally, charging rate is influenced strongly by the SOC of battery. EVs with lower battery SOC can absorb higher electricity and their charging rate decreases gradually as their battery SOC increases. In addition, charging in relatively higher temperature (summer) results in higher charging rate, therefore shorter charging time can be achieved. Lithium-ion batteries are generally charged employing a constant current (CC)-constant voltage (CV) method. Charging under higher temperature leads to higher charging current, therefore shorter charging time can be realized.
