Lithium-ion cell balancing using buck-boost converter

Abstract

The lithium-ion battery has gained considerable attention in Electric Vehicle sectors compared to the conventional lead-acid battery. It became commercially popular and used due to its salient characteristics such as high terminal voltage, energy density and power density of a single cell. However, if there is no proper power regulation during the process of both charging and discharging, the life span of the batteries will significantly decrease and leads to undesirable results such as fire or explosion at times which become a major drawback of lithium-ion (Li-ion) batteries. Proper power regulation is essentials and battery management system (BMS) are employed to circumvent these problems. SOC estimation, cell balancing, and thermal management are the common subsystems of battery management system (BMS). These subsystems are required to perform in real time and under conditions of rapid charging and discharged. Cell balancing is very crucial subsystem of the BMS which will efficiently prolong the battery life span. Thus, not only does the cell balancing method cover the task of protecting the cells, it also involves the task of equalizing charges between the cells. In electronic devices, the most common cell protection mechanism used is interruption of the charging and discharging process of the battery in order to prevent the battery from reaching its maximum and minimum permissible voltage. The charge imbalance among batteries occurs in the form of unequal voltages along the series connected batteries. The two major categories of cell balancing methodologies are active methods and passive methods. In this project, both categories of cell balancing will be studied extensively, and an efficient and suitable converter based active method is proposed and simulated using MATLAB Simulink.