The individual cells in a battery pack naturally have somewhat different capacities, and so, over the course of charge and discharge cycles, may be at a different (SOC). Variations in capacity are due to manufacturing variances, assembly variances (e.g., cells from one production run mixed with others), cell aging, impurities, or environmental exposure (e.g., some cells may be subject to additional heat from nearby sources like motors, electronics, etc.), and c.
needs two key things to balance a battery pack correctly: balancing circuitry and balancing algorithms. While a few methods exist to implement balancing circuitry, they all rely on balancing algorithms to know which cells to balance and when. So far, we have been assuming that the BMS knows the SoC and the amount of energy in each series cell.
A battery pack is out of balance when any property or state of those cells differs. Imbalanced cells lock away otherwise usable energy and increase battery degradation. Batteries that are out of balance cannot be fully charged or fully discharged, and the imbalance causes cells to wear and degrade at accelerated rates.
This unbalanced pack means that every cycle delivers 10% less than the nameplate capacity, locking away the capacity you paid for and increasing degradation on every cell. The solution is battery balancing, or moving energy between cells to level them at the same SoC.
Battery cell balancing brings an out-of-balance battery pack back into balance and actively works to keep it balanced. Cell balancing allows for all the energy in a battery pack to be used and reduces the wear and degradation on the battery pack, maximizing battery lifespan. How long does it take to balance cells?
What is a battery pack?
A battery pack is a collection of battery cells packaged into an application-specific format. These can be as small as a single cell or as large as thousands of cells arranged in series and parallel configurations, along with any associated electronics and mechanical components. A battery cell is the smallest energy-storing unit of a battery.
Why is SoC balancing important in EV battery pack?
After performing cell balancing, each cell's SoC reaches 60 % (average SoC) which signifies that all cells have reached to same level or balanced. Therefore, SoC balancing is crucial in EV battery pack to increase the usable capacity. Fig. 3. Charge among five cells connected in series before and after SoC balancing.