Battery Management Systems for Large Lithium-Ion Battery Packs
Section 5.6 Addenda
The individual chargers for each cell could be mounted directly on the cells, and even be built into the cell boards in a distributed BMS.
Usually, individual chargers are small AC-DC power supplies, powered by the line AC voltage; they could be small DC-DC converters, powered by a common DC bus; That bus could be powered, for example, by a single AC-DC converter powered by the AC grid, or by a distributed DC source such as solar panels. If this DC bus is connected to the battery terminals, then this implementation has in effect the same circuit as a battery-to-cells active balancer (188.8.131.52.2.3).
A disadvantage of distributed charging is that, during charging, the BMS has a hard time calculating the SOC of each individual cell, and therefore the SOC of the overall battery. The output current of each charger is different, and normally unknown to the BMS; unless the BMS has a current sensor for each cell, it cannot do Coulomb counting to determine cell SOC. All that a BMS can do is to guess the SOC during charging, and then calibrate the SOC based on cell voltage after charging is completed.