energies Article Management System for Large Li-Ion Battery Packs with a New Adaptive Multistage Charging Method † Ricardo Velho, Miguel Beirão, Maria do Rosário Calado *, José Pombo, João Fermeiro and Sílvio Mariano Instituto de Telecomunicações, Universidade da Beira Interior, 6201-001 Covilhã, Portugal; ricardovelho_94@hotmail.com (R.V.); mdbeirao@gmail.com (M.B.); jose_p@portugalmail.com (J.P.); fermeiro@ubi.pt (J.F.); sm@ubi.pt (S.M.) * Correspondence: rc@ubi.pt; Tel.: +35-127-532-9760 † This paper is an extended version of our paper published in Proceedings of the 2016 IEEE 16th International Conference on Environment and Electrical Engineering (EEEIC), Firenze, Italy, 7–10 June 2016. Academic Editor: Rodolfo Araneo Received: 14 February 2017; Accepted: 21 April 2017; Published: 1 May 2017 Abstract: Among the wide diversity of existing technologically mature batteries, lithium-ion (Li-ion) batteries have become popular because of their longevity, high energy density, high efficiency and lack of memory effect. Differential charging of cells with age has turned balancing management systems into an important research subject. This paper proposes a new battery management system (BMS) to improve the capacity usage and lifespan of large Li-ion battery packs and a new charging algorithm based on the traditional multistage method. The main advantages of the proposed system are its versatility and ability to implement different charging and balancing methods in a very accessible way. The combination of charging methods with balancing methods represents an evolution when compared with other works in the literature. Keywords: battery charge equalization; cell balancing; battery management system; large Li-ion battery pack 1. Introduction The longevity of a battery charge is nowadays a big issue for people who are usually outdoors. Electric Vehicles (EV), a worldwide growing market, are pretty dependent on battery capacity and usage, for EVs will only go as far as their battery allows [1,2]. Home battery-powered devices that can store energy from either local renewable sources or from the grid are also a promising technology highly dependent on battery usage patterns [3]. The need to interconnect multiple cells in series in order to obtain the required voltage levels, coupled with the existence of intrinsic and extrinsic differences between cells, results in a lack of uniformity that reduces usable capacity, lifetime and performance. Although parallel cells are self-balanced, this does not happen when they are in a series configuration [4,5]. This intrinsic (internal) non-homogeneity between cells is due mainly to small variations in the manufacturing process, such as different capacities, volume, internal impedance and different rates of self-discharge, characteristics that worsen with usage and battery age. The main extrinsic (external) factor is temperature non-homogeneity along the battery pack, which leads to different rates of self-discharge and consequent declines in performance. Some battery balancing methods proposed in the literature aim to create a system capable of applying a charging algorithm [6]. The dissipative resistors method adopted in this paper is based on the most frequently used balancing system due to its simplicity, cost, efficiency, volume, weight, robustness and reliability [7]. Energies 2017, 10, 605; doi:10.3390/en10050605 www.mdpi.com/journal/energies