Design and implementation of a fast charger with SOC estimation technique for LiCoO<inf>2</inf> battery

Abstract

This paper explores a fast charger based on microcontroller for LiCoO2 battery module. The main structure of the proposed system is the power factor corrector with a full-bridge phase-shift converter, its power factor upgrade close to 1.0, as well as to change the charging strategy according to the battery module's state of charge. Furthermore, the full-bridge phase-shift converter control chip communicates with battery management system via the I2C interface, to modulate the full-bridge phase-shift converter charging strategy to short the charging time and improve the battery lifespan. All the experimental results are also provided. In addition, the proposed charger system has universal input voltage specification and power factor correction function, the overall system efficiency is maintained around at 79.4% to 87%. Furthermore, we directly capture the related data of the battery cells from the battery management system via the I2C interface, and then through the open-circuit voltage method integrating the Coulomb integral method to find the lowest state of charge of the battery cell as a benchmark charge to adjust charging strategy. The pre-charge current is used when the SOC of the battery is lower than 15%. And then we employ the constant current charging if the SOC is from 15% to 75%. Finally, the charging strategy of the last phase will change to constant voltage charging to avoid the overcharging phenomenon.