*3.6. Fire Detection and Suppression System*

The fire detection and suppression system are a set of components used to ensure the safety of the place where it is installed, as well as that of people who transit internally and in the vicinity of the BESS. For this, the system is configured to have quick and efficient responses, ensuring agility to contain/extinguish the fire, as well as ensuring the evacuation of individuals.

The minimum elements that the fire detection and suppression system must include are:

	- -Smoke detector;
	- -Temperature detector;
	- -H2 and H2S detector if the technology is lead.

#### *3.7. HVAC*

The HVAC system regards the basic functions of the climatization system, allowing the environment to be in the right conditions for safe and efficient operation. Among the components that make up the HVAC are:


• Air conditioning (AC): used to artificially cool the place, controlling the temperature, and preventing it from becoming high. In addition, this equipment usually has filters, which carry out the removal of impurities and contaminants from the air.

These systems are essential for the proper functioning of the BESS, since by controlling the temperature, leaving it close to the most efficient temperature of the components (25 ◦C), it increases the productivity of the system. Furthermore, it promotes oxygenation of the place, air filtration, and reduction of air pollutants and the proliferation of fungi/mold.

#### *3.8. UPS*

The UPS is a secondary power system, which provides emergency power to the load when the primary supply is interrupted. As opposed to generators, the UPS operates very quickly, avoiding interruptions in the power supply.

In general terms, the UPS is made up of converters and batteries, which may or may not have a bypass switch. With respect to BESS, its load is not all the components of the system, but those that must always be kept in operation, allowing that in case of failure some action can be taken.

#### **4. Results and Discussion**

In this topic, the power smoothing and power factor correction functions are analyzed, as well as the approach of results and discussions of the data obtained using the two operating modes.

#### *4.1. Power Smoothing Application*

The results related to power smoothing are analyzed mathematically through the Maximum Power Variation (MVP) indicator. The active power smoothing technique performance of wind turbines is numerically evaluated. The MVP indicator corresponds to the maximum power variation in the wind generation rated power within an established time interval. Energy companies and system operators widely use this indicator from different European countries to restrict wind generation fluctuations, limiting the MVP to 10% in 1 min and 10 min intervals [23,24].

In the present article, a 5 min time interval (MVP5) is used, in which the calculation is performed from the difference between the maximum and the minimum power curve values in the specified interval and, according to that, the rated power of the generation to which the BESS that is connected is obtained. For example, considering a 50 MW wind generation rated power and a power curve whose difference between the highest and lowest value is 10 MW during the 5 min interval, the MVP is 20%. Thus, the lower the MVP value, the better the power smoothing quality. In an ideal case (i.e., a constant curve), the MVP would be 0% for any evaluated interval.

The BESS operating principle is performed through the EMS control system for the power smoothing function. The generation active power on the bus where the BESS is connected is verified. When the EMS verifies the 500 kW variation in a 60 s window, the system acts, absorbing or supplying active power, depending on the current generation status, that is, increasing or decreasing. Figure 7 illustrates a BESS operation based on the power wind generation variation.

In Figure 7, when the wind generation (blue curve) decreases in an interval of 60 s, the BESS supplies active power (orange curve). When wind generation increases, the BESS absorbs active power. The negative sign of active power means that the BESS is providing power and the positive sign of power implies that BESS is absorbing power.

The BESS performance operating in power smoothing mode connected in parallel to a group of wind turbines with 50.4 MW rated active power is illustrated in Figures 8 and 9. These figures show the generation curve behavior and its smoothing. Data from different days are shown.

**Figure 7.** Real-time BESS operation based on power generation variation. The measurement was carried out on 28 July 2021.

**Figure 8.** Active power of smoothed wind generation. Real-time measurement performed on 31 August 2021.

**Figure 9.** Active Power of Smoothed Wind Generation. Real-time measurement performed on 6 September 2021.

The blue curve indicates the power of the generation without BESS usage, while the smoothed curve is shown in orange. It is observed that the smoothed curves have smaller peaks and valleys and more attenuated curves.

The MVP index is used to evaluate wind generation power smoothing numerically. This analysis has better precision to evaluate power smoothing performed by the BESS in the present wind farm. Thus, in percentage terms, the smoothing effect results with the most significant gains points are presented in Table 1 (measurement in Figure 8) and Table 2 (measurement in Figure 9).

It can be seen from Table 1 that the MVP5 index, with the application of BESS, showed a considerable improvement in different time intervals. The best-obtained result for the 31 August 2021 day was an approximate 3.97% power fluctuation reduction, from 11:20 to 11:25 and 13:10 to 13:15. On the 6 September 2021 day (Table 2), the best result was a 3.97% reduction from 12:25 to 12:30. Different time intervals can be seen in Figures 8 and 9.

**Table 1.** Main indicators from the 31 August 2021 day.



#### **Table 1.** *Cont.*

**Table 2.** Main indicators from the 6 September 2021 day.


#### *4.2. Power Factor Correction Application*

The power factor is an energy utilization index whose adequate control in wind generation is significant, not only from an electrical energy point of view but also because it is monitored, in the case of Brazil, by the National Electric System Operator, and the power generator may incur fines. In this case, the BESS compensates for the excess reactive power, bringing the power factor within the regulatory limit (currently, in Brazil, the limit power factor is 0.95 in the PCC between wind generation and the transmission grid).

The EMS checks the power factor information generated by the wind turbines in the bus connected to the storage system. A power factor reduction (less than 1.00) activates BESS to operate with capacitive or inductive characteristics, depending on the wind generation power factor behavior (inductive or capacitive).

Figure 10 illustrates the BESS operation behaving with capacitive characteristics when the power factor measured at the bus is less than one (1.00). Therefore, according to the EMS programming, the system acts by injecting reactive power, trying to correct the power factor to the unit value (1.00). In Figure 10, the left scale refers to the system's reactive power (blue legend), and the right scale refers to the power factor value (orange legend) measured on the bus that connects the BESS to the group of wind turbines. It should be noted that the negative sign for reactive power means that the BESS is operating in capacitive mode and the positive sign in inductive mode.

**Figure 10.** Real-time BESS operation in the power factor correction function. The measurement was carried out on 25 March 2021.

Figure 11 illustrates the BESS operation on 23 March 2021, where it is seen that the system remains without acting while the power factor is unity (1.00). The BESS works by compensating reactive power when there is a drop in the power factor, aiming to establish the unit value. Figure 12 illustrates the operation of BESS on 19 April 2021, where it is seen that the system operates in both capacitive and inductive modes.

**Figure 11.** Real-time BESS operation in the power factor correction function. The measurement was carried out on 23 March 2021.

**Figure 12.** Real-time BESS operation in the power factor correction function. The measurement was carried out on 19 April 2021.

From the 19 April 2021 measurement data (Figure 12), it is possible to graphically characterize the resulting power factor behavior, considering the BESS performance, as illustrated in Figure 13. It can be seen from Figure 13 that the BESS corrects the power factor at different instances of time, aiming at the unit value (1.00), and thus helps to prevent the power factor from falling below 0.95.

**Figure 13.** Power factor resulting from the application of BESS. The measurement was carried out on 19 April 2021.

#### **5. Conclusions**

From the measurement analysis, it is observed that the power smoothing function implemented in the EMS does not present problems regarding the operating logic and operating time and shows satisfactory results. It was seen that the BESS manages to smooth the wind generation power with gains of up to 3.97% (measurements recorded in Tables 1 and 2) according to the MPV5 indicator. It is noteworthy that this result is considered satisfactory since the BESS rated power is 1 MW, and it is connected to a 50.4 MW wind generation.

From the measurements, it is observed that the BESS usage in power smoothing mode contributes to reducing power fluctuations at the point that connects the power output of the wind farm and the transmission line, generating improvements in the wind farm energy quality.

The power factor correction function performance analysis implemented in the BESS EMS shows that this function does not present problems regarding its operating logic and operating time. It was seen that BESS acted by correcting the power factor whenever necessary, reducing losses to the wind farm.

It should be noted that the constant growth of wind generation should amplify the effect of power fluctuation in transmission, distribution, and microgrid systems. Thus, wind generation should increasingly impact the operation and energy quality of electrical systems. The use of a BESS operating in active power smoothing mode represents a way to circumvent this problem and enable the use of intermittent renewable energy sources.

**Author Contributions:** Conceptualization, N.K.L.D., A.C.M.S. and A.S.M.V.; methodology, N.K.L.D., A.C.M.S. and A.S.M.V.; software, N.K.L.D.; validation, A.S.M.V., W.d.A.S.J., G.R., C.D. and P.R.; formal analysis, N.K.L.D., A.C.M.S. and A.S.M.V.; investigation, N.K.L.D., A.C.M.S., A.M.A.M. and A.S.M.V.; resources, G.R.; data curation, N.K.L.D. and A.S.M.V.; writing—original draft preparation, N.K.L.D., A.C.M.S., A.S.M.V. and W.d.A.S.J.; writing—review and editing, N.K.L.D., A.S.M.V., P.R., A.M.A.M., J.F.C.C., Y.L. and C.D.; visualization, P.R. and G.R.; supervision, A.S.M.V., W.d.A.S.J., A.M.A.M., J.F.C.C., Y.L. and P.R.; project administration, G.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Program of R&D of the National Electricity Regulatory Agency (ANEEL) and CPFL Energy. This work is related to the Project "PA3026—Insertion of Storage System in Multiple Configurations to Support Wind Generation".

**Acknowledgments:** This research was carried out by the R&D Program of the National Electric Energy Agency (ANEEL) and CPFL Energia. This work is related to the Project "PA3026 – Insertion of Storage System in Multiple Configurations to Support Wind Generation". The authors thank the R&D Program of ANEEL and CPFL Energia for all the incentives to this Research and Development.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

