Active Balancing to Improve the Efficiency and Sustainability of Battery Management Systems

The rapid growth of renewable energy, electric vehicles, and distributed energy storage has heightened the need for reliable battery management. One crucial challenge is the imbalance of voltage and capacity between cells and modules, caused by manufacturing differences, ageing, thermal gradients, and wiring resistance. These imbalances reduce usable capacity, lower efficiency, and may affect safety. This thesis studies and develops two types of active balancing circuits. The first work presents an inductor-based cell-to-pack balancing topology. It can operate over a wide voltage range and is compatible with various battery chemistries. The circuit uses low-side gate drivers and does not need isolated supplies or expensive driver ICs. It can balance multiple cells simultaneously with a controllable current that is independent of the imbalance level. Experimental tests on a five-cell lithium-ion battery pack demonstrate that the design is effective under both charging and discharging conditions. The second work proposes a coupled-inductor pack-level balancing topology. This design utilises only one switch and a few passive components per module, making it compact and cost-effective by employing local hysteresis control. The circuit achieves high balancing current without circulating losses. A scaled-down prototype with five series cells verifies that the topology can equalise voltages quickly and is suitable for modular and distributed systems, including cases with hot-swappable or reused packs. Together, these contributions give a practical framework for both cell-level and pack-level balancing. The results show that efficient and low-cost balancing can be achieved without relying on complex controllers or special integrated circuits. The work also points to future development, including continuous-conduction-mode operation for higher-voltage packs, tests on larger systems, and applications in second life and grid-connected energy storage.