Energy Conservation Versus Charge Conservation Law for Modeling and Analyzing Cell Equalizers

Battery system technology has gained increasing attention following the electric vehicles (EVs), renewable energy systems, and power electronics developments. Subsequently, equalization systems have been introduced to address the series-connected cells' charge imbalances, reducing the batteries' lifetime, reliability, capacity, and safety. To evaluate the performance of battery equalizers on a significantly large-scale systems, mathematical models have been introduced as the most effective tools. Compared to the conventional mathematical models that normally assume the amount of charge flowing in and out of cell equalizers is conserved based on the conservation of charge (CoC) principle, in this article, it is shown that conservation of energy (CoE) is a more accurate approach to analyzing and modeling the behavior of equalizers. To simply calculate the stored energy in batteries, an equivalent capacitance calculation method is used. Furthermore, to increase the accuracy of the model, the battery's internal resistance is also considered and a linearized model for batteries is developed. Using CoE and the linearized battery model, the behavior of battery cells during the equalization process is estimated with high accuracy. The proposed CoE model results are compared with the conventional CoC model and eventually verified by simulations and experiments.