Optimized Control Strategy for Inductor-based Cell Equalizers

The occurrence of imbalance conditions within the cells of a battery pack can be reduced or mitigated by an active cell equalization circuit integrated in the Battery Management System (BMS), which transfers energy between the most charged cells and the least charged ones in the pack. However, incomplete knowledge on the performances and range of operability in real-world scenarios is still limiting the adoption of active equalizers for lithium-ion battery systems in different fields of application. In this paper, among the different architectures presented in literature for active cell equalizers, the multi-inductor configuration has been investigated. For the generalized category of inductor-based configuration, an analytical model has been developed by taking into account the static and dynamic parasitic parameters of the components of the equalization circuit as well as the operating conditions of the cells. According to the model equations, optimal control techniques have been proposed, named as Constant-Frequency Control (CFC) and Variable-Frequency Control (VFC), for maximizing the performance of the balancing process in terms of efficiency and equalization speed. These control strategies can be easily implemented in state-of-the-art hardware. Numerical analyses have been carried out for validating the applicability of both control algorithms and comparing their performances in terms of equalization time and efficiency.