  A selection switch based cell-to-cell voltage equalizer requires only one
dual-port dc-dc converter shared by all the cells. A cell-to-cell voltage
equalizer is proposed that utilizes a capacitively level-shifted Cuk converter
and low-frequency cell selection switches. The absence of isolation transformer
and diodes in the equalizer leads to high efficiency, and the use of
low-frequency selection switches significantly reduces the cost of the drive
circuits. A low-frequency cell selection network is proposed using bipolar
voltage buses, where the switch count is almost half, compared to the existing
low-frequency cell-to-cell equalizers for the case of a large number of cells.
A novel approach for cell voltage recovery compensation is proposed, which
reduces the number of operations of the selection switches and the equalization
time. The proposed equalizer is implemented with relays and verified with an
8-cell Li-ion stack. The developed prototype shows the efficiency of over 90\%
and good voltage balancing performance during charging, discharging, and
varying load conditions. Experimental results also show about one order of
magnitude reduction in the number of relay switchings and a significant
reduction in equalization time using the proposed voltage compensation.
