Characteristics of cell voltage equalization circuit using LC series circuit in charging and discharging states

Series connections of cells of energy-storage devices such as electric double-layer capacitor (EDLC) and lithium-ion battery result in voltage imbalance in each cell because of the nonuniform properties of the individual cells. Previously, the authors proposed a novel cell voltage equalization circuit using LC series circuit. This paper shows the characteristics of the cell voltage equalization circuit using LC series circuit in charging and discharging states. In the charging state, external power supply is operated in 0.50A constant current mode (CC mode) and 9.00V constant voltage mode (CV mode). In the discharging state, electronic load operated in -0.50A CC mode and 3.00V CV mode. An experimental cell voltage equalization test using the proposed equalization circuit was performed for eight series-connected EDLC modules whose initial voltages were intentionally imbalanced. Experimental results demonstrated that the proposed equalization circuit could be the voltage of each cell connected in series modules equalized as time progresses in the charging state or discharging state. In addition, the standard deviation of each cell voltage was reduced to a sufficient low value below 10mV after finite time.