Electric vehicles (EV) are widely viewed as an essential technology for energy-saving and environmentally sustainable transportation. As the new traction requirements, critical energy sources of EV, lithium-ion (Li-ion) battery pack is drawing a vast amount of attention for its advantages, such as compact volume, large capacity, higher energy density, and better safety.
Single battery cells are serially and parallelly connected to make a battery stack to achieve higher voltage and capacity. However, the charging and discharging process need to stop as soon as any cell reaches its maximum limit or working threshold (below absolute threshold). Due to this, the capacity of the battery pack is limited by the imbalance in the cells of the pack. This reduces the energy usage efficiencies and shortens the lifetime of the battery pack.
Therefore, battery cell balancing is a basic, but essential function of a Battery Management System (BMS) and is necessary for battery packs. The following image provides a basic idea about
There are two popular ways of balancing, namely passive balancing and active balancing. The conventional passive balancing method prevents the bleeding of excess energy from cells into heat, while in active balancing there is a transfer of the excess energy into energy-depleted cells. Both typologies have their respective pros and cons. This blog will cover the important aspects of complete cell balancing.
Before diving into balancing, it’s important to understand the basic concepts of battery packs. The state of charge (SoC) is an important parameter for cell balancing. The SoC is nothing but the level of charge of an electric battery relative to its capacity. The balancing decisions are taken based on SoC. The aim is to have the same SoC for each and every battery at any given time. There are multiple algorithms used in BMS software to calculate accurate SoC to make decisions about balancing parameters.