Consideration about novel cell voltage equalization circuit for battery / EDLC

When using lithium-ion batteries or electric double-layer capacitors (EDLCs) as a storage module for electric vehicles, the cells of those storage devices are often connected in series. When a number of cells of the storage devices are connected in series, the cell voltage imbalance occurs by individual specificity such as the capacity, the rate of self-discharge, internal impedance, and temperature. In the state of the cell voltage imbalance, the amount of available electrical energy of total cells is decreased. Therefore, cell voltage equalization circuit is essential in order to derive maximum performance of lithium-ion battery or EDLC. This paper proposed the novel cell voltage equalization circuit for battery and EDLC. The proposed circuit not uses resistors; thus, the efficiency of the cell voltage equalizing operation can be improved. In addition, only one inductor and sensor are used in this circuit. Therefore, the cost of circuit can be reduced. Moreover, it can limit the current value of each battery cell in the voltage equalizing operation by use of only one current sensor. This paper explained the operation scheme, and conducted the characteristics comparison with the conventional circuits. Moreover, the effectiveness of this circuit was examined in simulation and experiment. The experiment was conducted using the three and eight EDLC cells (1.5F); and each cell voltage was equalized within finite time. In addition, the standard deviation of each cell voltage was reduced to a sufficient low value below 10mV after finite time. Therefore, the each cell was equalized in sufficient i.e. the effectiveness of the proposed circuit was shown.