Design and Control of Electrical Vehicle Battery Management System /

Abstract

In series connected lithium-ion battery packs, the cell-imbalance limits the optimum utilization to store energy during charging as well as discharging. The possible reasons are different state of charge (SOC), self-discharging rates, different capacities of cells, internal impedance, different coulombic efficiency of cell etc. Generally, active, and passive balancing techniques are employed to balance the series connected lithium-ion cells. The known parameters to differentiate balancing techniques are complexity of the circuit, balancing time, overall efficiency, and cost. This article proposes a direct cell level bypass balancing technique for a series connected cell based on the switch matrix to optimize the balancing time and the efficiency of the system. An alternate route to each series connected cell have been proposed to balance any cell of the battery pack while the charging and dis-charging operation of the battery continued. The proposed algorithm is very flexible as it allows to set any balancing setpoint from top to bottom as per requirement. The decision parameter to control the balancing process can be voltage, SOC, or both. The experimental setup validates the real-time operation balancing circuit of a battery pack module containing the 13-series connected lithium-ion cell. Different test cases are validated and compared with the simulation results.