*3.1. Description of the Real SCESS Module on Which this Study Is Based*

The unit module of SCs is made up of 8 drawers connected in series as shown in Figure 3. Each of the drawers has, in turn, 30 units of BCAP3000 cells connected in series. The main electrical characteristics of each cell are a nominal voltage of 2.7 V, capacity of 3000 F, and energy of 3 Wh. Therefore, the nominal capacity of the cabinet was 11.7 F and the total energy available was 500 Wh. If each cell is discharged to half its voltage, the total energy available is <sup>1</sup> <sup>4</sup> of the total energy. Despite this fact, and as mentioned in the previous point, the minimum working voltage of each cell was set at half the nominal voltage so that the performance of the DC/DC converter that connects the SCESS with the DC bus does not decrease considerably. Therefore, the theoretical operating voltage range of the cabinet was approximately 381-636 V. The cabinet was provided with 16 electronic boards to measure the voltage evolution of each cell. Another 30 temperature measurement channels were also used to monitor the maximum temperature of the cells and check it did not exceed 65 ◦C. Analog measurements of voltage and temperature were monitored due to a Concerto F28M35H52C microcontroller commercialized by Texas Instruments (12500 TI Blvd., Dallas, Texas 75243 USA) that was placed inside the same cabinet. This microcontroller acted as a web server to access the temperature and voltage measurements via the internet.

The cabinet had a cooling extractor turbine located in its upper part. The rotation speed of this turbine varied depending on the temperature in the cells. Additionally, each of the cells has a hardware protection system so that the cells did not exceed their maximum voltage. In addition, this system allows the total voltage to be balanced so that it is distributed equally among all the cells. Figure 3a shows the state of the cabinet during a balancing process.
