Cell equalisation circuits: A review

Large Li-ion battery packs are an enabling technology for electric vehicles, smart homes and the smart grid. Keeping the individual cells that make up the battery pack balanced reduces the loss of capacity over time and reduces the chances of damaging the pack by over charging/discharging cells. This paper presents a review of the basic charge equalisation circuits categorised as capacitor, inductor or transformer based. The paper highlights improvements and variations made to these basic circuits by researchers and provides a general comparison. The paper proceeds to discuss the difficulties in directly comparing performance of different CECs (charge equalisation circuit) and the ambiguity of the industrial requirements of a CEC. Finally the paper presents possible areas of research to further improve the charge equalisation process.