A Li-Ion Battery Charger With Variable Charging Current and Automatic Voltage-Compensation Controls for Parallel Charging

To preferably regulate the charging current and decrease circuit complexity for parallel charging, a battery charger with variable charging current (VCC) and automatic voltage-compensation (AVC) controls is presented. Based on the battery voltages, the VCC control not only dynamically maximizes the charging currents in both the trickle current (TC) and constant current (CC) stages but also prevents from damaging multiple batteries. Thus, the VCC control realizes safe charging and reduces charging time for parallel battery packs in the TC and CC stages. Owing to the battery's parasitic resistance, a conventional charger changes from CC to constant voltage (CV) stage without approaching the rated voltage of the battery packs. The AVC control estimates the parasitic resistance and determines the proper transition timing from the CC to CV stage. Therefore, the duration of CC stage is prolonged and the CV charging time is reduced. Thanks to the VCC and AVC controls, the proposed battery charger can achieve charging time reduction and charging safety simultaneously. The experimental results verify that the periods of CC and CV stages are extended and shortened, respectively, and charging currents are maximized to the predefined values in the TC and CC stages. The maximum efficiencies in the CC and CV stages are up to 96.4%. Furthermore, compared to charging dual battery packs with conventional control, the proposed controls can save about half of total charging time.