Charge shuttling with ultracapacitors for fast equalization of power lithium-ion battery

While charging or discharging the Li-ion battery of electric vehicles, cell equalization tries to restore all cells in the battery to an equal sate of charge in order to prolong the battery lifetime and to insure safe battery operations. This paper presents an equalization scheme for charge shuttling with ultracapacitors to efficiently control the bidirectional equalization process. The scheme development is significantly more involved in order to shorten equalization time in cells capable of generating high power in the fast charge/discharge mode. A prototype of twelve high power Li-ion cells with two most notable connections is implemented. The test results show that the proposed scheme can dramatically reduce equalization time and it can be effectively achieved for each cell in the strings during fast charge/discharge mode.