Evaluation and comparison of active cell balancing methods using energy storing elements
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Date
2022-09
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G.B. Pant University of Agriculture and Technology, Pantnagar, District Udham Singh Nagar, Uttarakhand. PIN - 263145
Abstract
In recent years the popularity of using lithium-ion batteries for energy storage purposes has risen a lot. However, the range of lithium-ion batteries available in the market is very small and for higher power requirements a significant number of cells are to be connected in series and parallel combinations. But when the cells are connected in series the problem of imbalance arises among them. Over the time, imbalance causes cell deterioration and reduced efficiency, therefore cell balancing becomes necessary in order to make sure the safe and reliable operation of lithium-ion batteries. The functionality of cell balancing is integrated within a Battery Management System. Cell balancing can be done in two ways i.e., passive balancing and active balancing. In passive balancing the excess charge is dissipated through a resistive element until all the cells come in balance with each other and in active balancing the excess charge is redistributed from higher energy cell to lower energy cell by using an external energy storing element such as an inductor, capacitor etc. In this work, capacitor-based active cell balancing has been studied because they have a simpler controlling mechanism as well as their implementation costs are less. More specifically, in this work, the implementation and comparison of switched capacitor, double-tiered switched capacitor, and chain-structure switched capacitor based balancing techniques have been done. The modelling of these techniques has been done in MATLAB/ Simulink and results are obtained for a series combination of 4 number of lithium-ion cells having 3.7V and 2.6A ratings with initial SOC variation as 15% and 8%. The cells are considered to be balanced when the maximum SOC difference between them reaches 1%. The results show that the double-tiered balancing technique takes the least time to balance the cells as compared to the switched capacitor and double chain-structure based techniques.