Comparative Study of the State of Charge (SoC) Balancing Techniques for Battery Power Module Configurations

The concept of the battery power module (BPM) has recently gained increased interest where the battery cells are decoupled from each other by connecting each cell with a lowpower DC-DC power converter. Accordingly, the output of BPMs can be connected in series and parallel to meet the required load voltage and power. In such systems, State-of-Charge (SoC) equalization is achieved by changing the rate of charge/discharge of each cell by controlling the duty cycle of the corresponding converter in BPM. Different types of DC-DC converters and control algorithms have been adopted in BPM architecture. The SoC estimation is generally acknowledged as one of the most important functions in the battery management system for lithium-ion batteries. Therefore, this paper comprehensively reviews the different control techniques presented in the literature to deal with BPM. The comparison includes the required number of sensors, the number of controlled variables, and its capability to achieve SoC balancing during both charging and discharging.