**7. Demonstration test**

**Figure 7.** Developed load leveling concept utilizing EVs and their used batteries.

136 Modeling and Simulation for Electric Vehicle Applications

curves of the next day (defined as day starting from 00:00 to 24:00).

by the EVs for load leveling.

with low price, and potential energy storage.

To forecast both load and possibly generated RE, EMS initially sends a request to meteoro‐ logical agency to deliver the local weather forecast information. This weather information is very crucial for calculating the electricity which can be potentially generated by RE, such as PV and wind. Because the amount of RE generation is significantly smaller than the total load, in this study, this generated electricity from RE is used directly for peak-cut, hence it will be delivered directly and consumed entirely without being stored in the battery. Moreover, the weather information is also used to forecast the fluctuating load of the office building, especially to calculate the demand of air conditioning (cooling and heating) and lighting. The outputs from this first step include the predicted power generation from RE and daily load

As the building load and possibly generated electricity from RE have been predicted, EMS will calculate the achievable load leveling (peak-cut) for the next day. In order to realize it, EMS sends a request to VIS to calculate and send the information related to the available EVs, including their battery SOCs, which will potentially participate for the load leveling program. This information is required to estimate the total available electricity which can be supplied

In order to perform the given request by EMS, VIS initially collects the traveling schedule from the EV drivers (planned departure time and predicted arrival time). Next, EMS forwards this information, as well as calculates the total availability of EVs and their batteries, together with basic information including EV's ID. This registration of traveling schedule is conducted up to 24 hours before the planned departure. Finally, using the data from the first and second steps, EMS is able to estimate the peak-cut threshold which can be applied for the next day.

In this study, a peak-cut threshold is determined as the maximum electricity which is pur‐ chased from the electricity grid. To calculate this peak-cut threshold, some important factors need to be considered including price of electricity at the corresponding time, contracted power capacity, possibly generated electricity from RE, available electricity supply from other sources

**Figure 8** shows the schematic diagram of the demonstration test bed developed in this study. Solid and dotted lines represent the electricity and information flows, respectively. In addition, **Figure 9** shows the pictures of the developed test bed. This demonstration test bed was constructed in the factory area of Mitsubishi Motors Corporation which is located in Okazaki, Aichi prefecture, Japan. Due to limited number of EVs and used EV batteries in this study, this test bed is connected to the electricity of the main office building (office building is considered as BEMS), and not to the whole electricity of the factory. PV panels having total maximum capacity of 20 kW is installed at the rooftop of the test bed as RE generator. In addition, five Mitsubishi EVs, i-Miev G, are participating in this demonstration test. The drivers are the employees who are working in the factory and EVs are used for commuting purpose. There‐ fore, EVs are basically available during working hours, especially during the day. They are parked and plugged to charging stations installed in the test bed. Furthermore, five used EV batteries are also employed as stationary battery. These used EV batteries are basically detached from the same type of EVs after about one year usage.

**Figure 8.** Schematic diagram of the developed test bed.

**Figure 9.** Overview of the developed system involving PV, EVs, and used EV batteries.


**Table 1.** Specifications of the developed test bed.

**Figure 8.** Schematic diagram of the developed test bed.

138 Modeling and Simulation for Electric Vehicle Applications

**Figure 9.** Overview of the developed system involving PV, EVs, and used EV batteries.

EMS is controlling the balance of both demand and supply of the main office building and test bed. EMS also forecasts and measures the demand of the office building. In addition, VIS is also developed as an independent system which communicates with EVs and transmits the received information to EMS. **Table 1** shows the detailed specifications of the developed demonstration test bed.

The drivers submit their daily traveling plans to VIS up to one day before the scheduled departure. To facilitate this, a web-based system has been developed facilitating the drivers to input and check their traveling plan from any computers or mobile devices. If EVs are not connected to the designated charging stations of EMS, such as in motion, EVs send their data to VIS in an interval of 10 s wirelessly. In addition, VIS transmitted the received data from EVs to EMS simultaneously. EMS receives EV data from VIS and weather information from meteorological agency. Although the weather information is received basically one day before, meteorological agency will update these data automatically once there is any renewal or correction in the weather information.

Used EV batteries are utilized for peak-shift. Charging of used EV batteries is practically performed from midnight to morning (00:00–06:00). Threshold for charging and discharging of both EVs and used EV batteries is set to SOC 90% and SOC 40%, accordingly. In addition, load leveling is designed to be conducted during afternoon peak-load time starting from 12:00 until 18:00 (6 hours duration) because the total amount of potentially available electricity from EVs and used EV batteries is limited and very small compared to the total load of the office building. In addition, to diminish the effect of ambient temperature on charging and discharg‐ ing behaviors of used EV batteries, the storage room of used EV batteries is controlled to have a temperature of 25 °C throughout the year at.

The load of office building is estimated as the sum of the base load and fluctuating load, especially the air conditioning demand. The air conditioning demand is calculated using historical data for several previous years and forecasted ambient temperature received from meteorological agency. The demand of office building in certain typical time, *L*<sup>t</sup> , can be simply approximated as follows:

$$L\_{\iota} = L\_{\boxtimes} + f\left(\left[T\_{\alpha\iota} - T\_{\Box\tau}\right]\_{\iota}\left(\Lambda\tau\right)\right) \tag{1}$$

where *L*BS, *f*, *T*OA, *T*ST, and Δ*τ* are the base load for 30 min interval (kWh) of the office building, functional relationship, outside ambient temperature (°C), room temperature inside the office building (°C), and time shift (h), respectively.

The available electricity from EVs, *P*EV, which are in motion and not plugged in to the charging poles can be estimated as the correlation of SOC and the remaining distance (both are received from VIS), and can be represented as follows:

$$P\_{EV,l} = \left(SOC\_{EV,l} \times C\_{EV} - d\_i \times \eta\_{EV} \right) - SOC\_{min} \times C\_{EV} \tag{2}$$

where SOCEV,*<sup>t</sup>* , *C*EV, *dt* , *η*EV, and SOCmin are SOC of each EV (%), EV battery capacity (kWh), remaining travel distance to the designated charging station (km), power consumption of EV (kWh km−1), and minimum SOC threshold for discharging (%), respectively.

To calculate the peak-cut threshold, a day load duration curve is initially created using the historical data of the averaged office building load for the same month in the last year. A peakcut threshold, *P*thr, can be approximated using Equation (3). **Figure 10** shows the illustration of a day load duration curve.

$$\begin{aligned} \text{for } L\_u &> P\_{ubr} \\ \Sigma L\_u &= n \left. P\_{ubr} + \Sigma P\_{av,m} + \Sigma P\_{hu,m} + P\_{pv} \end{aligned} \tag{3}$$

where *P*bat, *n*, and *m* are available power from used EV battery (kWh), number of load higher than peak-cut threshold, and number of EVs and used EV batteries, respectively.

In general, a load duration curve lines up all the loads in a descending order. Therefore, in this demonstration test, a day load duration curve is created by sorting all 30 min duration of office building loads from the largest to the smallest loads. Therefore, the plotted area represents the total electricity consumed by the office building for a day (starting from 00:00 to 24:00). Furthermore, the generated electricity from PV panels is directly delivered to the building without being managed by EMS to be stored in the battery. In addition, the total electricity which can be obtained from connected EVs, used EV batteries, and PV panels is plotted on the top of a day load duration curve for the corresponding day while its bottom is kept to be straight at the same value of load. Therefore, the created straight line is a peak-cut threshold which is used in load leveling.

**Figure 10.** Typical load duration curve and the calculated peak-cut threshold.
