Active battery cell equalization based on residual available energy maximization

Abstract

The residual available energy (RAE) of a battery pack is an important parameter for determination of the amount of energy left in the battery pack. The RAE is defined as a function of the cell's initial state of charge (SOC) discharge current cell capacity and internal resistance. Battery management systems achieve active equalization through balancing either the SOC or the terminal voltage of battery packs. Recent research discovered that these equalization schemes cannot maximize RAE of the battery pack due to the variation of internal resistances and capacities of the cells in the pack. On the other hand terminal voltage equalization is not applicable for batteries having a flat SOC-open-circuit voltage curve. This paper introduces the framework to calculate the RAE of a battery pack incorporating the variation of internal resistance and capacity of the individual cells in a pack. It further proposes a novel active battery cell equalization technique based on an RAE maximization scheme. The effectiveness of the proposed equalization scheme is validated through experimental results with a comparison of the energy utilization efficiency. The solution methodology and the results are discussed in the paper.