Battery BMS Equalization Technology: In-depth Analysis of Active Equalization and Passive Equalization

At a time when the new energy field is booming, battery technology, as the core support, has attracted much attention. Battery management system (BMS) plays a critical role in it, and battery balance technology is one of the key functions of BMS. This article will explore the two core battery BMS equalization technologies, including active equalization and passive equalization, analyze their principles, advantages and disadvantages, and application scenarios, and help readers fully understand the mysteries of battery equalization technology.

Why do batteries need balance technology

The battery pack is usually composed of multiple single cells in series. However, due to differences in manufacturing processes, different usage environments, and changes in the characteristics of the battery itself, these single cells will experience inconsistencies in voltage, capacity, etc. during actual use. If not corrected, this inconsistency will accumulate with the recycle of the battery, which may eventually lead to overcharge or over-discharge of some batteries, affecting the performance of the entire battery pack, and even causing safety issues. The introduction of equalization technology aims to adjust the voltage or energy of each single battery to balance, extend the service life of the battery pack, and improve the overall performance and safety of the battery pack.

Active balance: a powerful tool for efficient energy management

Active equalization is an advanced equalization method. Its core principle is to actively transfer the energy of single cells with higher energy in the battery pack to single cells with lower energy through specific circuits (such as bidirectional DC-DC converters, transformers, etc.) to realize energy reallocation and equalization.

Advantages

• High energy utilization: Active equilibrium avoids the waste of energy through energy transfer, which greatly improves the energy utilization efficiency of the battery pack. Energy utilization can be improved by around 30% compared to passive balancing, which is especially important for large battery systems (e.g., electric vehicles, energy storage systems, etc.) that require efficient energy management.
• Fast equalization speed: It can achieve the balanced state of the battery pack in a short time, especially suitable for scenarios where the individual cells in the battery pack have a large difference or high requirements for the balanced speed.
• Bidirectional adjustment: not only can it be balanced during charging, but it can also be dynamically adjusted according to the state of the battery during discharge, so as to better maintain the consistency of the battery pack.

Disadvantages

• The circuit is complex and the cost is high: Active equalization requires additional complex circuits, control chips, and energy storage and conversion components, which makes the hardware design of the entire BMS system more complex and the cost increases.
• High requirements for control accuracy: In order to achieve accurate energy transfer and distribution, the active equalization system requires high-precision sensors, controllers and complex control algorithms, which puts forward high requirements on the control accuracy and stability of the BMS.

Application scenarios

Due to its excellent performance, active balance technology is widely used in areas that require strict battery performance and life, such as electric vehicles, power tools, high-end energy storage systems, etc. In electric vehicles, active equalization can ensure that the battery pack always maintains good consistency under frequent charging and discharging cycles and high-power output conditions, extends the service life of the battery pack, and improves the vehicle's power performance and range.

Passive balance: a simple and practical basic solution

Passive equalization is to use the method of parallel resistors in the battery pack to consume the excess electrical energy of a single cell with a higher voltage in the form of thermal energy, so that the voltages of each single cell tend to be consistent.

Advantages

• Simple circuit and low cost: The implementation of passive equalization only requires a resistor and corresponding control switch to be connected in parallel to each single battery. The circuit structure is relatively simple, the hardware cost is low, and it is easy to design and implement.
• Mature technology and high reliability: This technology has been used in the battery market for many years. After a lot of practical verification, it has high technological maturity and high reliability

Disadvantages

• Low energy utilization: The excess electricity is dissipated in the form of thermal energy, causing energy waste and reducing the overall efficiency of the battery pack. Especially in large-capacity battery packs, this energy waste problem is more obvious.
• Slow equalization speed: Relying on the discharge process of the resistor to achieve equalization, the speed is relatively slow. For single cells with large differences in the battery pack, it may take a long time to achieve the equalization state.
• Only suitable for charging process: It can only play a role in the charging process of the battery and cannot effectively balance the adjustment during the discharge process.

Application scenarios

Passive equalization technology is often used in occasions where it is more cost-sensitive, has relatively low battery performance requirements and is small in size, such as consumer electronic products (such as mobile phones, tablets, etc.), low-cost energy storage systems, and some small electric equipment. In these applications, its simple and reliable characteristics can meet basic battery balance requirements while reducing the overall cost of the system.

Comparative analysis of active equilibrium and passive equilibrium

From the above comparison, we can see that active balance and passive balance have their own characteristics and advantages and are suitable for different application scenarios.

The integration and development of two balanced technologies

In practical applications, in order to give full play to the advantages of active balance and passive balance and make up for their respective shortcomings, some advanced BMS systems have begun to explore the integrated application of the two. For example, in the battery management systems of some electric vehicles, a strategy of combining active equalization and passive equalization is adopted. During the daily charging and discharging process, active balance is the main focus, and the energy of each single battery is quickly and effectively adjusted to maintain the consistency of the battery pack; and when the vehicle is left to stand for a long time or undergoes regular maintenance, passive balance is assisted to optimize the battery pack in depth to ensure the overall performance and life of the battery pack. This fusion solution not only improves the performance and safety of the battery pack, but also takes into account the cost and system reliability.

Future development trends

With the continuous development of battery technology and the increasing requirements for battery performance and life, battery BMS equalization technology is also constantly innovating and improving. In the future, battery balance technology will develop in the following directions:

• Higher energy utilization efficiency: Continuously optimize the active equalization circuit design and control algorithm, improve the efficiency and accuracy of energy transfer, and minimize energy loss.
• Faster equalization speed: Develop higher-performance equalization circuits and devices to improve the response speed and adjustment capabilities of the equalization system, and achieve fast and real-time battery equalization.
• Smarter balanced strategy: Develop intelligent balanced control strategies with the help of advanced technologies such as artificial intelligence and machine learning. By analyzing and learning the historical data and real-time operating status of the battery pack, and automatically adjusting the balance parameters and strategies, the refined management and balance control of the battery pack are achieved.
• Deep integration with other technologies: Battery equalization technology will be deeply integrated with the battery's thermal management system, energy management system, etc. to form a more complete and efficient battery management solution, and comprehensively improve the performance, safety and reliability of the battery system.

Battery BMS equalization technology is crucial to ensure the performance, life and safety of the battery pack. Active balance and passive balance are two core balance technologies, each with its characteristics and applicable scenarios. In practical applications, rational selection and application of balance technology, or exploring a fusion solution of the two based on specific needs is of great significance to fully utilize the performance potential of the battery pack and extend the service life of the battery pack. With the continuous development and innovation of technology, battery balance technology will provide stronger support for the development of the new energy industry, promote the wider application of battery technology in various fields, and help achieve a green and sustainable energy future.