A critical review of battery cell balancing techniques, optimal design, converter topologies, and performance evaluation for optimizing storage system in electric vehicles

Electric Vehicles (EVs) release no tailpipe emissions, making them a cleaner and more environment friendly alternative to common internal combustion engine (ICE) vehicles. With the advancement of EV technologies, lithium-ion (Li-ion) battery technology has emerged as the most prominent electro-chemical battery in terms of high specific energy and specific power. The Li-ion battery pack is made up of cells that are connected in series and parallel to meet the voltage and power requirements of the EV system. Due to manufacturing irregularity and different operating conditions, each serially connected cell in the battery pack may get unequal voltage or state of charge (SoC). Without proper cell balancing, serious safety risks such as over-charging and deep discharging in cells may occur. Considering the significant contribution of cell balancing in battery management system (BMS), this study provides a detailed overview of cell balancing methods and classification based on energy handling method (active and passive balancing), active cell balancing circuits and control variables. The DC-DC converter based balancing circuits (used to redistribute the charge among the cells in the battery pack) are the key component in the cell balancing as its conversion efficiency affects the overall performance of the EVs. Therefore, a detailed overview on different types of DC-DC converter-based cell balancing circuits is provided in this paper. In particular, this paper compares four (isolated/non-isolated) DC-DC converter-based cell balancing circuits including Duty cycle (bypassed) circuit based on balancing time during both charging and discharging operation. This review paper also covers detailed review of battery technologies, battery modeling, SoC estimation and performance optimization of BMS in EV application. The key is to highlight the characteristics, advantages and disadvantages, future challenges, and opportunities for advancing electric mobility. Finally, the challenges associated in BMS and battery cell balancing, potential area for improvement and future recommendation is provided to embrace the knowledge for development of high-performance EV.