A flexible Multi-Active Half-Bridge converter for active balancing of series-connected Li-Ion cells

Passive cell balancing is the most used technique to compensate the voltage mismatch in series-connected Li-Ion batteries, due to cost and simplicity. Active cell balancing is recently gaining more attention as it improves the battery capacity when the battery is ageing and, thus, lifetime when this is determined by the residual capacitance as in the electric transportation sector. This paper proposes a circuit configuration that can perform the active cell balancing using a multi-active half-bridge converter (MAHB) and a multi-winding transformer. The proposed solution has high flexibility due to different operating modes and a relatively simple circuit configuration. Depending on the State Of Charge (SOC) of each cell, the bidirectional power flows can be controlled between two arbitrary cells or between the entire string and a specific cell. A theoretical analysis is firstly carried out in order to understand the behavior of the circuit. Simulations and experimental results on a four Li-Ion cell prototype verify the validity of the proposed solution.