Author: Site Editor Publish Time: 2024-10-25 Origin: Site
In modern battery technology, we often encounter the term "battery balancing." But what does it mean? The root cause lies in the manufacturing process and the materials used in batteries, which lead to differences among individual cells within a battery pack. These differences are also influenced by the environment in which the batteries operate, such as temperature and humidity. These variations typically manifest as differences in battery voltage. Additionally, batteries naturally experience self-discharge due to the detachment of active material from the electrodes and the potential difference between the plates. The self-discharge rates can vary among batteries because of differences in manufacturing processes.
Let's illustrate this with an example: Suppose in a battery pack, one cell has a higher state of charge (SOC) than the others. During the charging process, this cell will reach full charge first, causing the rest of the cells that are not yet fully charged to stop charging prematurely. Conversely, if one cell has a lower SOC, it will reach its discharge cut-off voltage first during discharge, preventing the other cells from fully releasing their stored energy.
This demonstrates that differences between battery cells cannot be ignored. Based on this understanding, the need for battery balancing arises. Battery balancing technology aims to minimize or eliminate the differences between individual cells through technical interventions to optimize the overall performance of the battery pack and extend its lifespan. Not only does battery balancing improve the overall efficiency of the battery pack, but it also significantly extends the battery's service life. Therefore, understanding the essence and importance of battery balancing is crucial for optimizing energy utilization.
Definition: Battery balancing refers to using specific techniques and methods to ensure that each individual cell in a battery pack maintains consistent voltage, capacity, and operating conditions. This process is aimed at optimizing battery performance and maximizing its lifespan through technical intervention.
Importance: Firstly, battery balancing can significantly improve the performance of the entire battery pack. By balancing, performance degradation caused by the deterioration of individual cells can be avoided. Secondly, balancing helps extend the lifespan of the battery pack by reducing the voltage and capacity differences between cells and lowering internal resistance, which effectively prolongs the battery's life. Lastly, from a safety perspective, implementing battery balancing can prevent overcharging or over-discharging of individual cells, reducing potential safety risks such as thermal runaway.
Battery Design: To address the performance inconsistency between individual cells, major battery manufacturers continuously innovate and optimize in areas such as battery design, assembly, material selection, production process control, and maintenance. These efforts include improving cell design, optimizing pack design, enhancing process control, strictly selecting raw materials, strengthening production monitoring, and improving storage conditions.
BMS (Battery Monitoring System) Balancing Function: By adjusting the energy distribution between individual cells, BMS reduces the inconsistency and increases the usable capacity and lifespan of the battery pack. There are two main methods to achieve balancing in BMS: passive balancing and active balancing.
Passive balancing, also known as energy dissipation balancing, works by releasing excess energy from cells with higher voltage or capacity in the form of heat, thus reducing their voltage and capacity to match other cells. This process mainly relies on parallel resistors connected to the individual cells to shunt excess energy.
When a cell has a higher charge than others, the excess energy is dissipated through the parallel resistor, achieving balance with the other cells. Due to its simplicity and low cost, passive balancing is widely used in various battery systems. However, it has the drawback of significant energy loss, as the energy is dissipated as heat rather than being effectively utilized. Engineers usually limit the balancing current to a low level (around 100mA). To simplify the structure, the balancing process shares the same wiring harness with the collection process, and the two operate alternately. While this design reduces system complexity and cost, it also results in lower balancing efficiency and a longer time to achieve noticeable results. There are two main types of passive balancing: fixed shunt resistors and switched shunt resistors. The former connects a fixed shunt to prevent overcharging, while the latter precisely controls the switching to dissipate excess energy.
Active balancing, on the other hand, is a more efficient energy management method. Instead of dissipating excess energy, it transfers energy from cells with higher capacity to those with lower capacity using specially designed circuits that incorporate components such as inductors, capacitors, and transformers. This not only balances the voltage between cells but also increases the overall energy utilization rate.
For instance, during charging, when a cell reaches its upper voltage limit, the BMS activates the active balancing mechanism. It identifies cells with relatively lower capacity and transfers energy from the high-voltage cell to these low-voltage cells through a carefully designed balancer circuit. This process is both precise and efficient, greatly enhancing the performance of the battery pack.
Both passive and active balancing play critical roles in increasing the usable capacity of the battery pack, extending its lifespan, and improving overall system efficiency.
When comparing passive and active balancing technologies, it becomes clear that they differ significantly in their design philosophy and execution. Active balancing typically involves complex algorithms to calculate the exact amount of energy to transfer, while passive balancing relies more on accurately controlling the timing of switch operations to dissipate excess energy.
Throughout the balancing process, the system continuously monitors changes in the parameters of each cell to ensure that the balancing operations are not only effective but also safe. Once the differences between cells fall within a predefined acceptable range, the system will end the balancing operation.
By carefully selecting the appropriate balancing method, strictly controlling the balancing speed and degree, and effectively managing the heat generated during the balancing process, the performance and lifespan of the battery pack can be significantly improved.
