**1. Introduction**

The rapid expansion in socioeconomics has led to increasing global energy demand and usage. To balance the resulting widening energy deficiency, renewable energy distributed generation (REDG) is considered as an effective approach to solve the rising energy demand and other power system issues that are technical, economic and environmental in nature [1–3]. REDGs are generation technologies integrated at distribution networks near load users to satisfy immediate power demand, defer network upgrade, enhance power quality and reliability, diversify energy resources, and to reduce power losses, distribution and transmission loading, distribution and transmission costs and on-peak operating costs [4].

The battery energy storage system–photovoltaic DG (BESS/PVDG) is a viable renewable option because the resources are inexhaustible, complementary, economically

**Citation:** Owosuhi, A.; Hamam, Y.; Munda, J. Maximizing the Integration of a Battery Energy Storage System–Photovoltaic Distributed Generation for Power System Harmonic Reduction: An Overview. *Energies* **2023**, *16*, 2549. https://doi.org/10.3390/ en16062549

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

Received: 20 December 2022 Revised: 17 February 2023 Accepted: 24 February 2023 Published: 8 March 2023

**Copyright:** © 2023 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/).

profitable, environmentally friendly and bi-directional [5–8]. However, the power generated from BESS/PVDG depends on charge and discharge schedules of BESS, which is associated with high voltage rise or fall, and temperature and irradiation of solar energy that is intermittent in nature [6,9–11]. Hence, a substantial number of research studies have unanimously agreed/concurred that harmonics occur in the distribution system when BESS/PVDG units are absorbed due to the intermittent and variable nature of PVDG output power and the high variability of voltage and frequency of BESS schedules. In essence, current harmonics occur as a result of sudden disparity between the aggregate output power of BESS/PVDGs and other generations and the total power demand at an instant in a distribution system. The high rises and falls of the voltage and frequency from battery charge/discharge schedules may result in voltage harmonics [11].

The harmonic distortions are a troubling power quality issue for BESS/PVDG power generation, and they have significant consequences on the DNs. The extent of current harmonics is determined by the active output power from BESS/PVDGs. Thus, the magnitudes of current harmonics are enormous at utility-scale BESS/PVDGs penetration levels. The intermittency of PVDG units and the high voltage rise or fall from BESS/PVDG raise concerns on distribution system harmonic distortions, which have negative effects on power quality, stability and reliability of distribution systems [6,12,13]. The high harmonic contents in the power system lead to increased losses in system elements such as transformers and generating plants; economic costs such as productivity, energy and device/equipment losses; and fire hazards due to overheating of system elements [7,14,15]. The issues mentioned make the integration of a large-scale BESS/PVDG into the distribution systems difficult [6,15,16]. Meanwhile, the locations and sizes of BESS/PVDG units could either improve or impair the magnitudes current and voltage harmonic levels of the networks [17–19]. The mentioned issues make the solution of BESS/PVDG allocation problems formulated using simple mathematical models unrealistic. A realistic model, therefore, requires a dynamic model representation of the network, the use of multi-period planning horizon as well as all the necessary constraints. The problem then becomes a multi-objective one with a maximisation of renewable active and reactive powers into the DNs and a minimisation of the total cost subject to the capacity, investment, technical, stability and harmonic constraints throughout the planning horizon.

Several studies have been performed to proffer optimal solutions for the planning allocation of BESS/PVDG in distribution systems [11,13,16,20–23]. The studies on optimal planning of REDG allocation warrant detailed investigations on the prospects of BESS/PVDGs for generating power, the impact on the DNs, and the effects on the inadequate availability and rising cost of energy, the global economy and environment. Various researchers have reviewed some aspects of the BESS/PVDG allocation planning (BESS/PVDGs-AP) problem. Many solution algorithms, planning models, and emerging technologies deployed in BESS/PVDG-AP have been presented [24–28]. Zahraee et al. [24] presented an analysis of some artificial intelligence optimum plans used in the optimization and sizing of hybrid renewable energy systems. The main contribution of this work is the extensive penetration of renewable energy features for economic performance of the systems. The authors in [25] dealt with the review of some solutions that were used to improve the ability of the distribution system to cope with variable renewable energy source unpredictability such as energy storage technologies, PV and wind energy systems. This study concluded that battery energy storage and pump hydro energy storage are the most used technologies to improve the impact of the variable renewable power on distribution systems. A review presented by Hannan et al. [26] on the planning of BESS and renewable energy hybrid DGs discussed the optimal sizing objectives, various optimization models, the BESS system constraints together with their advantages and weaknesses. A detailed discussion of the BESS applications and shortage of optimal BESS sizing models could be identified as the strong point of this study. In [27], a review of the latest research developments and challenges on optimal planning of a BESS-PVDG connected distribution system was presented. The authors suggested key parameters in the process of optimal

planning for a PV–battery system such as economic and technical data, objective functions, energy management schemes, design constraints, optimization algorithms, and electricity pricing regimes.

In view of the contribution of the existing review works on the BESS/PVDGs-AP problem, this study is distinct in these ways:


Despite numerous reviews and studies on BESS/PVDGs, some aspects have not been adequately captured for investigation, review and research. These themes, bulleted above, are comprehensively treated in this paper.

The remaining parts of this paper are organized as follows: Section 2 presents the overview of harmonic components in the BESS/PVDG connected distribution networks. Section 3 details a review of various optimization models and techniques published in the existing research works and some promising algorithms that are recently introduced and used for solving BESS/PVDG allocation optimization problems. The methodological approach for curtailing the harmonic distortions in a BESS/PVDG connected distribution system is presented in Section 4. The characteristics of all the models and techniques are compared, and their shortcomings are discussed under Results and Discussion in Section 5, to assist the researchers in choosing and applying them successfully and in a cost-effective way. Section 6 is the concluding part of the paper, and the recommendations for future research directions are also presented here.

### **2. Overview of Harmonic Components in BESS/PVDG Systems**

Power system harmonic distortion is a major issue for power utilities throughout the world. In recent times, statistical analysis reports have revealed that power system harmonics has become a very troubling power quality issue in BESS/PVDG systems. These harmonics have resonating impacts in generating other power quality problems in largescale BESS/PVDG [7,15,29–31]. The sources of harmonics produced in BESS/PVDGs are broadly classified into DC-link voltage harmonics, switching harmonics and grid voltage harmonics [7,32].

#### *2.1. DC-Link Voltage Harmonics*

The DC-link voltage ripples have become a major source of harmonics produced by BESS/PVDGs [32]. The DC-link voltage harmonics are generated by PVDGs due to solar irradiation intermittency and the high rises or falls of BESS voltage. Du et al. [32] illustrated this phenomenon with the experimental setup simulated in MATLAB Simulink. The experimental results in Figure 1 show that the harmonic distortion increases as DClink voltage increases. However, these harmonics are usually taken as constant in the analyses and designs of BESS/PVDG inverters. They are not always so in the practical sense. This accounts for the odd harmonic frequencies discovered in the spectrum of BESS/PVDG inverter's output current [33]. In addition, Mansor et al. [34] investigated harmonic generation in three-phase BESS/PVDG inverters and found that the secondorder harmonics in the DC link produced the third-order harmonic discovered on the AC side of the inverter. [34]. Many methods have been proposed by the researchers to eliminate the current harmonics generated by the DC-link voltage ripple [35–39]. Some of the proposed methods reduced the dynamic performance of the system, and many lack

quality information on the connection between the output current harmonics and DC-link voltage ripples [32].

**Figure 1.** Impact of BESS/PVDG DC-link voltage ripples on harmonics [32].
