Active Equalization and Cell Balancing Circuits for Battery Management System: An Overview

Battery management system (BMS) plays an important role in ensuring safe and efficient operation and long-term liveliness of the battery over thousands of charging cycles. Active equalization and cell balancing are crucial aspects of the BMS in electric vehicles (EVs), renewable energy sources (RESs) with energy storage systems (ESSs), and portable electronics. Generally, active equalization and cell balancing circuits are divided into transformer-based, inductor-based, capacitor-based, and converters-based circuits. Also, these active equalization circuits can be categorized into different categories, such as direct cell-to-cell (DC2C), adjacent cell-to-cell (AC2C), pack-to-cell (P2C), cell-to-pack (C2P), and any cell to any cell (AC2AC), based on their energy transfer methods. This paper provides an overview of different types of active equalization and cell balancing circuits for the BMS for both stationary as well as dynamic ESS applications. Then, the challenges and limitations associated with these active equalization circuits have been discussed. Finally, these active equalization and cell balancing circuits have been compared and summarized in terms of size, control, speed, and efficiency.