li ion 18650 battery pack BMS architecture, lithium battery management system BMS knowledge

　　li ion 18650 battery pack BMS architecture, lithium battery management system BMS knowledge. The power output of electric vehicles relies on batteries, and the lithium battery management system BMS is the core of it, responsible for controlling the charging and discharging of the battery and realizing battery status estimation and other functions. The lithium battery management system can ensure the safety of the power li ion 18650 battery pack, which is the primary task of the lithium power battery management system. Many people don't know anything about batteries and other related knowledge because they are not in this major. But now that hybrids and electric vehicles are so popular, if you don’t understand a little bit, it won’t make sense. This article will introduce the knowledge of lithium battery management system BMS to help you get rid of the situation of battery novice.

　　li ion 18650 battery pack BMS architecture

　　The topology structure of the li ion 18650 battery pack BMS hardware is divided into two types: centralized and distributed:

　　(1) The centralized type integrates all electrical components into a large board. The sampling chip channel has the highest utilization and daisy chain communication can be used between the sampling chip and the main chip. The circuit design is relatively simple and the product cost is greatly reduced. All acquisition wiring harnesses will be connected to the motherboard, posing greater challenges to the security of the BMS, and there may also be problems with the stability of daisy chain communication. It is more suitable for situations where the battery pack capacity is relatively small and the module and battery pack types are relatively fixed.

　　(2) Distribution includes a main board and a slave board. One battery module may be equipped with a slave board. The disadvantage of such a design is that if the number of cells in the battery module is less than 12, it will cause a waste of sampling channels (generally there are 12 sampling chips channel), or 2-3 slave boards collect all battery modules. This structure has multiple sampling chips in one slave board. The advantages are high channel utilization, cost saving, system configuration flexibility, and adaptability to different capacities and Modules and battery packs of different specifications and types.

　　The tasks of lithium battery management system BMS

　　The main task of the battery management system is to ensure the design performance of the battery system, which can be broken down into the following three aspects:

　　1) Safety, protect battery cells or battery packs from damage and prevent safety accidents;

　　2) Durability, allowing the battery to operate in a reliable and safe area and extending the service life of the battery;

　　3) Dynamic performance, maintaining the battery working in a state that meets the requirements of the vehicle.

　　Lithium battery management system BMS function

　　Generally speaking, the electric vehicle battery management system must implement the following functions:

　　1. Accurately estimate the state of charge of the power battery pack:

　　Accurately estimate the state of charge of the power li ion 18650 battery pack, that is, the remaining battery capacity, to ensure that the SOC is maintained within a reasonable range and prevent damage to the battery due to overcharge or overdischarge, thereby predicting how much remaining energy storage battery remains in the hybrid vehicle at any time The state of charge of an energy or energy storage battery.

　　2. Dynamically monitor the working status of the power battery pack:

　　During the battery charging and discharging process, the terminal voltage and temperature, charge and discharge current and total battery pack voltage of each battery in the electric vehicle battery pack (should be a power battery pack) are collected in real time to prevent the battery from overcharging or over-discharging. . At the same time, the battery status can be given in time, problematic batteries can be selected, and the reliability and efficiency of the entire battery pack can be maintained, making it possible to implement the remaining power estimation model. In addition, a usage history file for each battery must be established to provide information for further optimization and development of new batteries, chargers, motors, etc., and to provide a basis for offline analysis of system failures.

　　3. Balance between single cells and battery packs:

　　That is, balancing is performed between single cells and battery packs so that each battery in the battery pack reaches a balanced and consistent state. Battery balancing is generally divided into active balancing and passive balancing. Most of the BMS currently put into the market adopt passive equilibrium. Balance technology is a key technology of battery energy management system that the world is currently researching and developing.

　　Lithium battery management system failure

　　Battery management system failures include CAN communication failures, total voltage measurement failures, cell voltage measurement failures, temperature measurement failures, current measurement failures, relay failures, heater failures, and cooling system failures.

　　Line or connection failure diagnosis of line or connection failure is equally important to ensure driving safety and vehicle reliability. For example, due to the vibration of the vehicle, the connecting bolts between the batteries may become loose, the contact resistance between the batteries increases, and a virtual connection failure occurs between the batteries, resulting in increased energy loss within the battery pack, resulting in insufficient vehicle power and short driving range. In extreme cases, it can cause high temperatures, generate arcs, melt battery electrodes and connectors, and even cause extreme battery safety accidents such as battery fire.

　　During the operation of an electric vehicle, relative jumps may occur between single cells, causing the connecting piece between the two batteries to break. The electrical connection between the battery box and the electric vehicle is also a frequent source of faults. Electrical connectors are prone to virtual connections after long-term vibration, resulting in faults such as ablation and poor contact.

　　In summary, there are many factors to consider in battery management system circuits, especially those that determine packaging limitations. When packaging design ideas come together, it is also important to consider the structure of the electronic circuitry and information flow that may also have mechanical effects. As the central control idea of power batteries, the BMS control method directly affects the service life of the power battery and the safe operation and vehicle performance of electric vehicles. It has a significant impact on battery life and determines the future of new energy vehicles. A good lithium battery management system will greatly promote the development of new energy vehicles.

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