At present, the balancing schemes in lithium battery BMS management systems mainly include passive balancing and active balancing. Among them, passive balancing is favored by most BMS manufacturers due to its mature scheme and low cost. It is also the most widely used balancing method on the market. Active balancing, however, is limited in application due to its high cost and complex circuitry. Further expansion of its usage is needed.
What does passive balancing mean? Suppose the lithium battery pack is like a wooden barrel, and the battery cells are the individual wooden planks that make up the barrel. Due to manufacturing processes and usage wear and tear, the wooden planks of this barrel become uneven in length and shape.
Passive balancing means cutting all the wooden boards to the shortest length. This method is simple and straightforward but highly efficient. However, the remaining water (capacity) in the barrel will decrease. (Passive balancing uses the method of resistance heating and discharging to consume the "excess electricity" of high-capacity batteries, thereby achieving the purpose of balancing.)
What is active balancing like? Again, using the same bucket, active balancing involves using the leftover scraps to add to the short sections of the board to make them consistent. However, this method is quite cumbersome and inefficient. But the remaining water in the bucket will be much more than that in the case of passive balancing. (Active balancing involves transferring the excess electricity through energy transfer to the battery cells with higher remaining capacity, maintaining the consistency of the battery.)
With the current advancements in cell manufacturing technology and PACK process, the demand for passive balancing may gradually decrease, while active balancing will be increasingly applied in lithium battery packs to perform preventive maintenance and balance, maintaining the consistency of the battery pack and extending its service life.