L822 battery.The organizational structure, functions and operating mechanism of the power battery management system

　　The organizational structure, functions and operating mechanism of the power battery management system

　　There are many articles on the introduction of power battery management systems, which are quite technical and are basically incomprehensible to non-professional engineering and technical personnel. Focusing on the word "management", the following will introduce the organizational structure, basic functions and operating mechanism of the power battery management system, and popularize scientific knowledge in this aspect.

　　1. Understanding of power battery management system

　　(1) System: multiple individuals with certain functions are organized into a new unit according to certain requirements (rules). For example, multiple batteries are connected head to tail (or head to tail, tail to tail) to form a new unit.

　　(2) Management: For specific objects, in an area, clean up according to a requirement and organize according to certain rules. For example, the factory cleans and organizes items in the material warehouse according to certain requirements and rules.

　　(3) Power battery: an electrochemical storage device that provides electrical energy for electric vehicles.

　　(4) Power battery management system: related activities that manage the power system.

　　2. Organizational structure of power battery management system

　　(1) Minimum unit: refers to one section or one battery cell. There are currently three shapes of power battery cells: cylindrical, square, and flat.

　　(2) Basic unit: more than 3 single batteries are connected in parallel to form a new row of battery packs;

　　(2) Module: a large battery pack with more than 3 basic units connected in series;

　　(3) Battery pack: A box (usually made of metal) that encapsulates a large battery pack (module) and is required to be dustproof, waterproof, and equipped with an interface.

　　(4) Power battery management system function box: an integrated circuit function box with automatic measurement of current, voltage, temperature and communication modules.

　　Popular understanding is that the hardware structure and layout of an electric vehicle's power battery that has been offline have been solidified. In other words, the power battery management system no longer manages the battery hardware structure and layout.

　　3. Basic management functions of power battery management system

　　The hardware structure and layout of electric vehicle power batteries and product design work have been introduced before, but what are their management functions?

　　(1) Why does the power battery pack (system) need to be managed? The power battery pack (system) has two basic functions: one is charging and the other is discharging.

　　(a) Charging management: when can it be charged, when can’t it be charged, and is it fully charged? Do not overcharge etc.

　　(b) Discharge management: When should it be discharged? When should it not be discharged? Has the discharge been completed? Do not over-discharge, etc.;

　　(c) The working environment temperature of the power battery pack (system) must be monitored, and overheating and smoke must be monitored. If a safety hazard occurs, the alarm must be called. If a safety accident occurs, preparatory facilities must be activated for processing.

　　There are three levels of management functions:

　　(i) For the working status of the power battery pack (system), the relevant changes must be measured;

　　(ii) Analyze and judge the dynamic value of the relevant change amount. If it exceeds the normal value, an alarm must be issued;

　　(III) If the power battery pack (system) fails, relevant measures must be initiated, such as downgrading operation.

　　4. Mechanism of power battery management system

　　(1) Understanding of the mechanism

　　(a) refers to the structure and operating principle of the machine;

　　(b) The structure, functions and interrelationships of organisms;

　　(c) The processes and manner in which organizations or parts of a work system interact with each other.

　　(2) Introduction to the mechanism of power battery management system

　　①The three basic status quantities of the power battery pack (system): voltage, current, and temperature

　　(a) Voltage: Where there is electricity, there is an electric field. The electric field force is different at different locations in the electric field. Voltage is a measure of the ability of an electric field force to do work. Voltage is the driving force that drives the flow of electrons;

　　(b) Current is driven by voltage, and electrons flow from the negative electrode to the positive electrode of the power supply. Current refers to the amount of charge passing through the cross-section of a conductor in 1 second;

　　(c) Temperature: A physical quantity that expresses the degree of hotness or coldness of an object.

　　(Note: The voltage, current and temperature of the battery are the basis of the top-level calculation and control logic of the battery management system)

　　②Measure the comprehensive status of the power battery pack (system): SOC and SOH

　　(a) Remaining power (SOC): The full name is State of Charge. It represents the ratio of the remaining capacity of a battery after being used for a period of time or left unused for a long time to its fully charged capacity, usually expressed as a percentage. Its value range is 0~1. When SOC=0, it means the battery is completely discharged. When SOC=1, it means the battery is fully charged.

　　(b) Power battery health (SOH): It is the percentage of the battery's full charge capacity relative to its rated capacity. A new factory battery is 100%, and a completely scrapped battery is 0%.

　　(3) Difficulties in mechanism design of power battery management system

　　(a) How to measure voltage, current and temperature?

　　There are corresponding sensor products for voltage, current, and temperature. Sensors from different manufacturers have different quality, accuracy, and measurement error processing methods. Different manufacturers have their own unique technologies and processes. The basic principle is that you must choose products that meet vehicle specifications.

　　(b) Estimate of remaining power and health of power battery?

　　The theoretical models for estimating remaining power and power battery health vary from manufacturer to manufacturer, and the estimation error handling is also different. Different manufacturers have their own unique technologies and processes in their products. The basic principle is that you must have your own characteristics and core competitiveness.

　　5. Tesla power battery management system function box

　　①BMS adopts a master-slave architecture. The master controller (BMU) is responsible for high voltage, insulation detection, high-voltage interlocking, contactor control, external communication and other functions;

　　②The controller (BMB) is responsible for detecting the unit voltage and temperature and reporting it to the BMU;

　　③The BMU has a primary and secondary MCU design. The secondary MCU can detect the working status of the primary MCU and obtain control authority once its failure is discovered.

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