Citation: Miranda, J.P.D.; Barros, L.A.M.; Pinto, J.G. A Review on Power Electronic Converters for Modular BMS with Active Balancing. Energies 2023, 16, 3255. https://doi.org/10.3390/en16073255 Academic Editors: Danial Karimi and Amin Hajizadeh Received: 7 March 2023 Revised: 30 March 2023 Accepted: 4 April 2023 Published: 5 April 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/). energies Review A Review on Power Electronic Converters for Modular BMS with Active Balancing João P. D. Miranda 1, * , Luis A. M. Barros 1,2 and José Gabriel Pinto 1,2 1 Department of Industrial Electronics, University of Minho, 4800-058 Guimarães, Portugal 2 ALGORITMI Research Centre/LASI, University of Minho, 4800-058 Guimarães, Portugal * Correspondence: pg47332@alunos.uminho.pt Abstract: Electric vehicles (EVs) are becoming increasingly popular due to their low emissions, energy efficiency, and reduced reliance on fossil fuels. One of the most critical components in an EV is the energy storage and management system, which requires compactness, lightweight, high efficiency, and superior build quality. Active cell equalization circuits such as those used in battery management systems (BMS) have been developed to balance the voltage and state of charge (SoC) of individual cells, ensuring the safety and reliability of the energy storage system. The use of these types of equalization circuits offers several benefits including improved battery performance, extended battery life, and enhanced safety, which are essential for the successful adoption of EVs. This paper provides a comprehensive overview of the research works related to active cell equalization circuits. This review highlights the important aspects, advantages and disadvantages, and specifications. Keywords: active cell equalization; battery management systems; electric vehicles 1. Introduction The development of electric vehicles (EVs) is currently growing and is seen as one of the main technologies to reduce the environmental impact of transportation [1,2]. With the increase in the dependence on fossil fuel imports and rising oil prices, the search for alternatives to the traditional transportation system has become increasingly pressing [3]. The transportation sector is a significant contributor to global greenhouse gas emissions, accounting for over 25% of total emissions worldwide [4]. Within this sector, private cars such as passenger cars, sport utility vehicles (SUVs), and small vans are the largest source of emissions, accounting for roughly 60% of the total [5]. On the other hand, global greenhouse gas emissions are also increasing due to air traffic, leading to the research and study of aircraft electrification to improve the management of electrical power onboard aircraft and reduce gas emissions [6,7]. The replacement of fossil fuel-powered vehicles with electric vehicles holds the promise of a future with cleaner air and a reduction in the harm caused by humanity to the environment as well as to meet the Kyoto restrictions, which aim to limit greenhouse gas emissions and combat climate change [8]. The electronic industry is facing new challenges as the sales of EVs rapidly increase [9]. According to the research described in [10–12], the key focus areas for improvement include reducing the size of grid-connected battery chargers, developing dc–dc converters for the interface between sources and the direct current (dc)-bus, and creating new converter topologies for the traction system. Another crucial factor is energy storage. Energy is typically stored in a battery pack consisting of several groups of cells connected in se- ries/parallel [13,14]. To ensure that the batteries operate properly and within safe limits, they are usually equipped with an electronic battery management system (BMS) [15,16]. However, commercially available BMSs are quite rudimentary and mainly rely on passive cell balancing (putting a resistor in parallel with the most charged cells to dissipate energy until they have the same charge level as the other cells in the pack) [17,18]. The energy Energies 2023, 16, 3255. https://doi.org/10.3390/en16073255 https://www.mdpi.com/journal/energies