Coordinated operation algorithm of pack-chargers and cell-equalizers for SOC adjustment in second-life batteries

Abstract

Investment for battery energy storage systems (BESS) is rapidly growing. However, cost is still a major barrier. Since a retired battery pack from an electric vehicle can be re-utilized for BESS, second-life battery energy storage systems (SL-BESS) have become a promising option. However, SL-BESS applications require more intensive care in terms of battery maintenance due to the increase in the characteristic differences of aged cells. Therefore, the SOC adjustment process is essential both for maintenance and shipping. This study proposed a coordinated operation algorithm for the calibration process with an optimal processing time. In addition, the effects of pack and cell currents on adjustment speed have been investigated. Experimental results verify the performance of the calibrator by a sequence of test scenarios. The battery cells are equalized and adjusted to the target SOC level within a 14 mV error, while the processing time is reduced by 20% when compared to the traditional method.