**5. Integration of EVs and their used batteries to small-scale EMS**

The conceptual diagram of integration of EVs and used EV batteries in supporting the electricity in a small-scale EMS is presented in **Figure 4**. To take part in the ancillary services coordinated by EMS, there must be an initial contract between the EV owners EMS, either direct contract or aggregator-based contract through third entity such as an aggregator. Because of the mobility characteristic of EVs, their charging and discharging behaviors can be fully controlled by EMS in case EVs are connected to the designated charging stations. In addition, the used EV batteries are employed as stationary storage which are always connected to and managed completely by EMS. These used EV batteries are utilized mainly for peakshift. Therefore, they are charged when the electricity price is low, such as during night time, and discharged during peak-load time or when the electricity price is relatively high, such as noon time. Hence, the amount of electricity which is purchased from the grid during peakload time can be reduced, resulting in total low electricity cost.

**Figure 4.** Conceptual diagram of integration of EVs and their used batteries to small-scale EMS.

**Figure 3.** Relationship among charging rate, battery SOC, and charging time during EV charging in different seasons:

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.

(a) winter and (b) summer.

132 Modeling and Simulation for Electric Vehicle Applications

EMS is basically controlling all the electricity flows including demand and supply sides. Some types of small-scale EMSs include BEMS, FEMS, and HEMS. A direct contract scheme is adopted in this case. EMS requests the required information from different sources covering its own demand (load), weather information from meteorological agency, EV information from VIS, electricity condition in the community from CEMS, and grid electricity condition from utility. Regarding the weather information, EMS generally has a service contract with certain meteorological agency providing the weather forecast in a certain interval of time in a day. Based on the received weather forecast, EMS will estimate its own load, including base load and fluctuating load. The former is generally defined as the minimum load which is required to run the system for sequential 24 hours. Therefore, this kind of load is usually constant along the day and insignificantly effected by the weather or human behavior. On the contrary, the latter is determined as the load which is influenced strongly by the surrounding weather and human behavior. The fluctuating load includes air conditioning, heating, and lighting. Moreover, the possibly generated electricity from RE, such as wind and solar, is also predicted by EMS utilizing the weather information received from meteorological agency.

**Figure 5** represents the average total load of the office building, especially in Japan, in four different seasons. The highest total building load takes place in summer, and is followed by one in winter, due to air conditioning demand. In addition, building loads in both spring and autumn are almost similar, which are lower than one in winter. Furthermore, daily peak-loads occur twice in a day (weekday), i.e., before noon and afternoon peak-loads. This is because of the immediate drop of load following the lunch break for about 1 hour. The afternoon peakload mostly takes place in a longer duration, which is about 3 hours, and is higher than the before noon peak-load. Moreover, the highest value of peak-load during summer takes place during afternoon time (13:00–16:00) due to cooling demand. On the contrary, this highest value of peak-load moves to evening time (16:00–17:00) during other three seasons (autumn, winter, and spring) due to heating demand.

**Figure 5.** Average electricity loads for office building in different seasons.

EMS also receives the EV information from VIS including their position (GPS data), battery SOC, and predicted arrival time. In addition, VIS monitors and collects the information from its EV members wirelessly. It might be an independent service operator and a part of EMS or aggregator. It is responsible to communicate with each EV and provide the collected data to the EMS or aggregator in which VIS has a contract with. In addition, these data are used for coordinating both charging and discharging of EVs, maintaining the balance of electricity and avoiding any peak-load in EMS. Furthermore, VIS is also able to provide additional services to the EV drivers/owners concerning the available ancillary service programs which are being offered by EMS or aggregator. Hence, the EV owners can select according to their interests or conditions. Furthermore, EMS can request the electricity utilities to provide the information including the electricity condition and price in advance (such as one day ahead). This infor‐ mation is important to plan and optimize the electricity supply as well as calculate the amount of electricity which should be purchased from utilities. In addition, EMS also calculates the charging and discharging behaviors of both EVs and used EV batteries which are available according to the information provided by VIS.

**Figure 6** shows the assumed one day specific curve of EV battery SOC during a weekday. EVs are departed in the morning and they reach the destination (office building) at around 9 am. In this study, EVs are used for peak-cut during the afternoon peak-load due to higher peakload and limited number of EVs in a demonstration test. EV discharging is stopped in case that the peak-cut (load leveling) finishes or the SOC of EV batteries drops to minimum SOC (SOCmin). SOCmin might be determined by the EV drivers/owners, EMS, or aggregator. In addition, EVs leave the office building at around 6 pm with minimum battery condition (SOCmin). On the other hand, in case that the total building load is relatively low (such as in the morning, lunch break, and night) EVs might be charged to enhance their discharging capacity or extending their traveling.

**Figure 6.** Typical SOC state of EVs in weekdays (commuting).

latter is determined as the load which is influenced strongly by the surrounding weather and human behavior. The fluctuating load includes air conditioning, heating, and lighting. Moreover, the possibly generated electricity from RE, such as wind and solar, is also predicted

**Figure 5** represents the average total load of the office building, especially in Japan, in four different seasons. The highest total building load takes place in summer, and is followed by one in winter, due to air conditioning demand. In addition, building loads in both spring and autumn are almost similar, which are lower than one in winter. Furthermore, daily peak-loads occur twice in a day (weekday), i.e., before noon and afternoon peak-loads. This is because of the immediate drop of load following the lunch break for about 1 hour. The afternoon peakload mostly takes place in a longer duration, which is about 3 hours, and is higher than the before noon peak-load. Moreover, the highest value of peak-load during summer takes place during afternoon time (13:00–16:00) due to cooling demand. On the contrary, this highest value of peak-load moves to evening time (16:00–17:00) during other three seasons (autumn, winter,

EMS also receives the EV information from VIS including their position (GPS data), battery SOC, and predicted arrival time. In addition, VIS monitors and collects the information from its EV members wirelessly. It might be an independent service operator and a part of EMS or aggregator. It is responsible to communicate with each EV and provide the collected data to the EMS or aggregator in which VIS has a contract with. In addition, these data are used for coordinating both charging and discharging of EVs, maintaining the balance of electricity and avoiding any peak-load in EMS. Furthermore, VIS is also able to provide additional services to the EV drivers/owners concerning the available ancillary service programs which are being offered by EMS or aggregator. Hence, the EV owners can select according to their interests or conditions. Furthermore, EMS can request the electricity utilities to provide the information including the electricity condition and price in advance (such as one day ahead). This infor‐

by EMS utilizing the weather information received from meteorological agency.

and spring) due to heating demand.

134 Modeling and Simulation for Electric Vehicle Applications

**Figure 5.** Average electricity loads for office building in different seasons.
