**1. Introduction**

The growing concern about the environment and the depletion of fossil fuels has given rise to a new scenario to meet the energy needs of society: renewable sources [1,2]. Among the various renewable sources of electricity, wind generation has been presented as the most interesting and the fastest growing in the world [2,3]. According to the Global Wind Energy Council (GWEC) 2022 report, the wind industry had its second-best year in 2021, with nearly 94 GW of capacity added globally. Total global wind power capacity is now up to 837 GW, helping the world avoid more than 1.2 billion tons of CO2 annually—the equivalent of South America's annual carbon emissions.

The growth of wind energy in the world energy matrix is due to its advantages, such as: it does not emit greenhouse gases; it takes little time to build wind farms; it diversifies the electricity matrix; it is independent of the variation in fuel prices; it is easy to expand the capacity of wind farms; it provides new markets etc. [2]. However, due to the highly uncertain and variable nature of the wind, wind energy can present undesirable characteristics in its generation and impact the Electric Power Systems (EPSs). With an increasing share of EPSs, the uncertainty of wind energy and its power fluctuation will affect the ability of grid operators to balance generation and demand. Furthermore, the significant penetration of wind generation in the grid can harm the Power Quality, the dynamics, and the system reliability [2,4].

**Citation:** Dantas, N.K.L.; Souza, A.C.M.; Vasconcelos, A.S.M.; Junior, W.d.A.S.; Rissi, G.; Dall'Orto, C.; Maciel, A.M.A.; Castro, J.F.C.; Liu, Y.; Rosas, P. Impact Analysis of a Battery Energy Storage System Connected in Parallel to a Wind Farm. *Energies* **2022**, *15*, 4586. https://doi.org/ 10.3390/en15134586

Academic Editors: Luis Hernández-Callejo, Jesús Armando Aguilar Jiménez and Carlos Meza Benavides

Received: 10 May 2022 Accepted: 16 June 2022 Published: 23 June 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

According to [2,5], the main concerns regarding the connection of wind generation in electrical systems are related to the impact on the stability and Power Quality of the grid, the ability to compensate for active power fluctuations, and the impact on grid voltage, both short-term and long-term. To minimize some of these problems, additional flexible resources must be used to manage the variability and uncertainty of wind generation. Battery Energy Storage Systems (BESS) can be used to reduce power fluctuations, as well as provide ancillary services (voltage and frequency regulation), manage energy during disturbances (short circuits), and increase network reliability.

There is a wide range of possible BESS applications in the electrical sector, such as power generation, transmission, and distribution, and direct applications to the final consumer. However, it can be said that the attractiveness of each specific solution depends on the characteristics and needs of the applications. For example, BESS can be used for short-term power smoothing in wind farms in a generation. Using BESS, it is possible to mitigate the adverse effects of the power fluctuation in wind generation and, consequently, improve the Electrical Power Quality (EPQ) and the power grid operation. As for the final consumer, BESS can be used to perform arbitrage, charging the batteries during lower-priced hours, and discharging during higher-priced hours (i.e., during peak hours).

The BESS can be idle for a significant fraction of time, depending on the application. Thus, to make this solution more viable, it is possible to merge different applications. For example, BESS systems installed in more robust systems, such as the Brazilian National Interconnected System (SIN), can implement other services such as arbitrage, operating reserve, frequency control, voltage control, and black start. Thus, the merging of applications increases the use of BESS over time.

Energy storage systems have been widely simulated to reduce power fluctuations from wind generation with different control strategies [6–9], and [10] proposed using a storage system integrated into a wind system to reduce high-frequency fluctuations in the generated power, using filters to separate the operation of the inverter controllers and the storage system in the frequency domain. In [11], it is seen that to provide constant supply from a 39.6 MW wind farm, a 2 MWh capacity energy storage system was used to maintain consistent production for one hour and up to 103 MWh to provide consistent output for one day.

In [12], it is seen that the intermittent operation of renewable energy sources, faults occurrences, or PCC disturbances can cause voltage or frequency deviations, resulting in instability problems, which can become severe in weak power networks. In [12], a storage system was used to regulate voltage and frequency in microgrids.

There are many different papers which evaluate the power smoothing of wind generation through BESS. Among the recent papers, there are relevant talks about the problem of the power fluctuation in many different contexts and settings, such as the power smoothing in the context of transmission or distribution, different technologies of BESS, different types of power control for BESS, complementary applications for power smoothing, different settings of connection of BESS, and different ways to evaluate and present the results [2]. However, considering these different contexts and settings there are still topics to be explored and improved. Several papers do not verify the effects of power smoothing in wind generation, as well as do not use numerical indicators to evaluate the performance of the power smoothing techniques. Thus, the main contribution of this article is to analyze the effects of power smoothing in wind generation in a case study at the Campo dos Ventos Wind Complex located in João Câmara, Rio Grande do Norte (RN)—Brazil. The numerical indicator of Maximum Variation Power (MVP) is also used to evaluate the performance of the power smoothing techniques. The MVP indicator quantifies the largest power of wind generation within a predefined time interval.

Furthermore, this paper addresses, in a complementary way, the application of power smoothing, the analysis of the storage system operating in the power factor correction mode, and its impact on Power Quality for the Campo dos Ventos Wind Complex. Experimental results are performed to validate the performance of BESS.

#### **2. Project Description**

The purpose of the Research and Development R&D Project PA3026, entitled "Impact Analysis of a Battery Energy Storage System Connected in Parallel to a Wind Farm", is to study energy storage applications from different qualitative and quantitative perspectives. This project is formed by the group of institutions CPFL Energy (Light and Power Company of Sao Paulo State), Institute of Technology Edson Mororó Moura (ITEMM), Federal University of Pernambuco (UFPE), and PSR—Energy Consulting and Analytics.

Brazil still presents a relatively immature environment for the development of energy storage technologies. Faced with regulatory and even non-regulatory gaps, the R&D Project PA3026 seeks to resolve existing uncertainties about the applicability and effectiveness of services and assist recognition through adequate remuneration for these storage systems.

From this perspective, the project proposes to investigate the operationalization of several actions applied to a real wind farm. Among the main functions destined for the storage system identified in the project are produced power smoothing and power factor correction. These two proposals are tested with the operation of a BESS composed, among other components, by a set of Lithium Iron Phosphate (LFP) batteries, which is a lithium-ion battery technology with a capacity of 1 MW/1.29 MWh integrated into an electric power substation of a wind farm. The choice of this technology was due to the benefits that the LFP battery presents, such as: (1) high energy density (about 1932 W/L) [13], (2) high conversion efficiency (90~95%) [14], (3) low self-discharge rate, and (4) fast response time [13]. It should be noted that the service life (>2000 cycles) still needs to be improved and there are potential fire hazards [13,14].

According to [13], flow batteries are safe as they are non-flammable and have a long cycle life (2000 to 20,000 cycles) and do not depend on the depth of discharge. However, the energy density is low, occupies a large amount of land, and the conversion efficiency is low (65–85%) [15]. Hydrogen batteries have the highest specific energy (500–3000 Wh/L) compared to other storage systems and have a high cycle life (about 20,000 cycles). Although hydrogen batteries have a long-life cycle, they have a high initial cost [13]. The lead-acid battery is safe and reliable, but its energy density is low and its cycle times (300–3000 cycles) are limited [16].

The wind farm choice considered the capacity and arrangement of machines with different technologies. The Campo dos Ventos Wind Complex, located at João Câmara—Rio Grande do Norte (RN)—Brazil, a synchronous generator with a full converter and Double Powered Induction Generators (DFIG), was chosen. This farm has twenty-four turbines, each with 2.1 MW rated power, totaling 50.4 MW. Therefore, the 1 MW/1.29 MWh capacity BESS can be analyzed in terms of its real impact on the proposed objectives. The turbines and BESS are connected through a SCADA system. The simplified single-line diagram for the Campo dos Ventos Wind Complex is shown in Figure 1. The installation of BESS at the Campo dos Ventos Electric Substation (ES) is illustrated in Figure 2.

The main objectives of using the storage system are to smooth the wind production through instantaneous power injection and instantaneous power consumption, counterbalancing its instantaneous output and, consequently, removing variations introduced by the wind intermittence acting on each other the wind turbine.

Considering other storage system application options, it is expected to use the remaining storage capacity for reactive power compensation, firstly, to improve the power factor and, secondly, to improve the voltage with the consequent reactive power control.

**Figure 1.** Single-line diagram of the Campo dos Ventos Wind Complex.

**Figure 2.** Installation of BESS in the Campo dos Ventos Substation.
