A novel methodology to estimate the efficiency of supercapacitor-based active balancing architectures

Second-life lithium-ion batteries retrieved from electric vehicles are a very appealing resource for stationary applications such as smart grids. However, their performance is limited by the strong mismatch among their cells. Dynamic equalization is a very promising approach to maximize the second-life battery capacity, transferring charge from the best-performing cells to the least-performing ones. Even if this functionality is very similar to the active balancing approach used in first-life batteries, the dynamic equalization approach requires high-current DC/DC converters. Therefore, converter design is crucial for obtaining high efficiency in all possible battery states. A novel approach to determine in closed form the efficiency of a super-capacitor-based active balancing architecture was developed. It can estimate the efficiency of the system with comparable accuracy, but in a significantly shorter time than other methods presented in the literature. Such considerable advantages make the proposed approach a valuable tool for implementing optimization procedures, thus helping the designer in the selection of the components for the design of the active balancing circuit considered.