Cell Equalizers Modeling and Analysis Based on Energy Conservation Method

The use of energy storage systems (ESSs) has increased as a result of the zero-emission energy systems and electric vehicles growth. One of the main challenges regarding the series-connected ESSs is their voltage imbalances while charging and discharging, which result in over-charge or under-discharge and decrease the ESSs' lifetime. Therefore, different types of equalization systems have been proposed to mitigate this problem. One of the best large-scale equalization systems evaluation methods is the use of equalizer mathematical models. Conservation of charge (CoC) principle which states that the amount of charge flowing in a cell equalizer is equal to the amount of charge flowing out of it over the equalization process has been used to model the cell equalization systems so far. In this paper, it is shown that conservation of energy (CoE) is a more accurate method to analyze and model the equalizers because CoE method considers cells' voltage differences during the equalization process. Using CoE model, two important equalizer behavioral parameters which are equalization voltage and equalization time are estimated for two series cells with an interconnected buck-boost equalizer. The proposed CoE model results are compared with the conventional CoC model and eventually verified by simulations and experiments.