Preface Lithium-ion battery is the most widely used battery in the market. Its main purpose include power battery and energy storage battery. In practical applications, enough cells are usually connected in series to meet the high voltage demand and connected in parallel to meet the high capacity, but each cell in the battery pack is different, which will affect the performance and life of the whole battery pack. Nowadays, in order to avoid inconsistence in the battery pack, different battery-equalization methods are put forward. There are usually two methods of battery equalization, including keeping the state of charge between cells consistent and making the voltage between cells equal. At the same time, the equalization control strategy also includes active cell equalization and passive cell equalization. Compared with the passive equalizing strategies that dissipate energy, active cell equalization method transfers the energy between the cells, which is more efficient and requires shorter equalization time. Because of the advantages of active cell equalization strategies, it has attracted great interest from academia and industries. In addition, this book introduces the state-of-the-art active cell equalization control strategy for lithium-ion battery packs from the fundamental theories to practical designs. In particular, for different equalization topologies, different equalization control algorithms are used to realize the equalization of each cell in the battery pack. Of course, the same equalization topology can also adopt different equalization control algorithms to realize the equalization of each cell of the battery pack. In addition, charge equalization will also keep the SOC of all cells of the battery pack consistent. This paper mainly includes the following three parts: ? The first part (Chaps. 1–4) first explains that the key role of cell balance is to prolong the service life of battery pack and improve the performance of battery pack; next the battery-equalization system is summarized: the advantages and disadvantages of active equalization system and passive equalization system are compared, and the advantages of active equalization are emphasized, then some new equalizing algorithms of active equalization are introduced. Thirdly, several advanced active cell equalization topology models are introduced. Here, the activeequalization topology includes cell-to-cell, cell-to-pack, module-based and layerbased. At the same time, we perform an economic and performance comparison of the above topologies; finally, according to graph theory, we design the optimal active cell equalizing topology. ? The second part (Chaps. 5–8) designs a neural network-based observer and introduces the three equalization control algorithms based on part of the above topology. For cell-to-cell equalization topology, we first introduce a quasi-sliding mode observer to estimate the SOC value of each cell in the battery pack, then we introduce quasi-sliding mode control-based equalization strategy to realize cell-to-cell equalization, and use hierarchical control to achieve the balance of module-based cell-to-cell topology model. In hierarchical control algorithm, the top layer is the module-level equalizing control, and the bottom layer computes the controlled cell-level equalizing currents for different battery modules in parallel; besides, for cell-to-pack-to-cell equalization control, we divide the battery pack into several modules and introduce an improved module-based CPC equalization, based on the developed model, a two-layer MPC strategy is proposed, where the top-layer MPC controls the ML equalizers and the bottom-layer MPC designs the controlled CMC equalizing currents in each module. ? The third part (Chaps. 9 and 10) designs the two equalization control algorithms based on multi-module charger. For charging strategy of battery pack, the aim is to design a charger so that the SOCs of battery pack converge to the same value. That is, the batteries’ SOCs converge to the same desired value in the charging mode. In this part, firstly, we utilize IDA-PBC as bottom-layer controller to make the actual charging currents track their desired values designed by the top layer; secondly, we design a quadratic programming-based simultaneous charging strategy for battery packs, which realize the simultaneous equalization of different battery packs. Hangzhou, China November 2022 Jian Chen Quan Ouyang Zhisheng Wang