These SOA boundaries will ultimately be determined by the intrinsic chemistry of the selected lithium-ion cell and the temperature of the cells at any given time. This allows the BMS to possess nearly instantaneous sensitivity to extreme current peaks, such as a short-circuit condition that has not caught the attention of any resident fuses, but also be forgiving to high peak demands, as long as they are not excessive for too long.Įlectrical Management Protection: Voltageįigure 2 shows that a lithium-ion cell must operate within a certain voltage range. A BMS may incorporate peak current monitoring by integrating the current and after delta time, deciding to either reduce the available current or to interrupt the pack current altogether. However, this may be preceded to account for a sudden change of load conditions for example, an electric vehicle’s abrupt acceleration. A BMS providing current protection will certainly apply a maximum continuous current. Battery cell manufacturers usually specify maximum continuous charging and discharging current limits, along with peak charging and discharging current limits. Lithium-ion cells have different current limits for charging than for discharging, and both modes can handle higher peak currents, albeit for short time periods. In many cases, further derating may be applied to reside within the SOA safe zone in the interest of promoting further battery lifespan. Figure 1 illustrates a typical lithium-ion cell SOA, and a well-designed BMS will protect the pack by preventing operation outside the manufacturer’s cell ratings. The electrical SOA of any battery cell is bound by current and voltage. Monitoring battery pack current and cell or module voltages is the road to electrical protection. Battery pack protection management has two key arenas: electrical protection, which implies not allowing the battery to be damaged via usage outside its SOA, and thermal protection, which involves passive and/or active temperature control to maintain or bring the pack into its SOA.Įlectrical Management Protection: Current We’ll discuss how these two features work here. There are many BMS design features, with battery pack protection management and capacity management being two essential features.
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