Battery Management System and its Applications

15 BMS for an E-Bike

In practice, all manufacturers of E-bikes today rely on a storage solution with lithium-ion (Li-ion) technology. E-bikes reliability and effective distance covered with support of the battery strongly depends on the health and charging state of the battery. A common bike battery voltage today has a range between 24 V and 52 V nominal. The battery pack consists of individual cells connected in series. In general, the series-connected cells never behave in the same way, even if they belong to the same batch from the same manufacturer. They always partially differ in SoC, capacity, internal resistance, self-discharge rate, and temperature behavior. These differences will intensify with the age of the battery, usually due to a thermal imbalance in the pack. Due to the different rates of aging, the cells run further and further apart towards the end of their lives. Thus, to provide a dependable and high-performance solution for E-bike users, the battery pack should be in perfect balance. In other words, all cells should perform more or less the same. The requirement creates scope for a balancing system to be in place.

In a battery, the weakest cell determines the total capacity of the pack while the stronger cells still have some remaining capacity. Therefore, the load could never utilize the full capacity of the pack. In order to counteract this effect, passive voltage/charge balancing in Li-ion batteries has been frequently used in the past. However, today, ...