Interleaved Switching for Loss Minimization in Adjacent Cell-to-Cell Balancing Architectures

The cell-to-cell variation in capacity and impedance leads to a charge imbalance within the battery pack, which tends to degrade its various states and the available energy. Therefore, a Battery Management System (BMS) equipped with a charge equalization circuit (CEC) will enhance the overall performance of the pack, resulting in improved electric range and grid storage capacity. The adjacent cell-to-cell (AC2C) architecture has a higher equalization loss because charge distribution is limited between adjacent cells and the hard-switching operation of their connected CECs. A charge equalization algorithm where interleaved switching of CECs with variable duty control is proposed in this article. The proposed switching operation improves the equalization loss by regulating the equalization current (rms and average) relative to the balanced state of the individual cell. To study the equalization performance for diverse scenarios of imbalance, a 48 V, 20 Ah pack with AC2C buck-boost CEC is configured in the PLECS simulation environment, where the proposed algorithm has achieved around 32% reduction in equalization loss. For experimental validation, an 18 V, 10.4 Ah LCO battery pack connected to the BMS and a series AC2C equalization unit are developed for the balancing operations.