Design and Prototyping of Battery Management Systems for Lithium-ion Battery Packs

High-performance equalization circuits have to satisfy different requirements, including modularity, scalability, weight and volume, reliability, cost, hardware and software complexity. Currently, the design targets are mainly focused on minimizing the equalization time and the overall size of the circuit. This also implies the definition of a proper thermal management for dissipating the heat generated due to the high balancing currents that may be needed. However, literature and industry standards do not address the problem of the optimal sizing of the equalization circuits, which is strongly affected by the operating conditions of the battery pack as well as the parameter variations of the components adopted. The original contribute proposed in this dissertation regards the definition of design methodologies for passive and active equalization circuits that take into account for relevant aspects of both battery pack and power electronics components. Firstly, the real operating conditions of both individual cells and the overall battery pack have been considered in terms of cell technology, temperature, model calibration and voltage imbalances among the cells. Secondly, the real behavior of the components used for the specific equalization circuit and their parameter variations have be taken into account. In this way, a proper evaluation of the performance of the equalization circuits can be achieved by considering their functionalities in real operating conditions. In particular, design strategies have been proposed for four BMS architectures, one for each main equalization type, including passive, capacitor-based, inductor-based and transformed-based solutions. Moreover, a novel architecture for an active equalization circuit has been developed for the transformer-based equalizer, which allows for achieving a cells-to-cells energy transfer. Besides the development of design strategies for passive and active equalization circuits, real prototypes have been sized and implemented as well. In detail, a modular architecture for the passive equalizer of a 50HP electric kart and the novel active equalizer have been prototyped with the aim of validating their performance in real-world environments. These prototypes also allow for managing high-voltage battery packs or hybrid systems, which are composed by different technologies of batteries (second life applications). Moreover, a detailed comparison between the prototypes developed has been carried out in order to highlight their main features in different operating conditions, including charging, discharging and idle state.