BMS is an electric vehicle battery management system and is an important link between the vehicle power battery and electric vehicles. The BMS collects, processes, and stores important information during the operation of the battery pack in real time, exchanges information with external devices such as vehicle controllers, and solves key issues such as safety, availability, ease of use, and service life in the lithium battery system. The main function is to improve the utilization rate of the battery, prevent the battery from overcharging and over-discharging, extend the service life of the battery, and monitor the status of the battery. In layman's terms, it is a system for managing, controlling, and using battery packs.

　　Source of this article: Panda Hardware WeChat public account ID: xiongmaoyingjian

　　1. What is BMS?

　　Lithium-ion batteries have limited range of use;

　　For lithium-ion batteries, their ideal operating range is very limited and not wide. Therefore, lithium-ion batteries must be managed during application, especially in power battery application scenarios.

　　2. Security issues

　　Distortion

　　Swelling

　　Flaming on fire

　　Explosion

　　Overvoltage (overcharge), overcurrent and overtemperature will bring a series of safety hazards to lithium-ion batteries.

　　3.Performance management

　　The external characteristics of lithium batteries are closely related to their own status (SOC/SOH/temperature) and ambient temperature.

　　4.Lifespan

　　Temperature factor environmental factor

　　Voltage factor (SOC & ΔSOC) Voltage factor (SOC window)

　　Current factor Current factor

　　High SOC and high temperature environments will aggravate the irreversible capacity loss of the battery.

　　5. Consistency

　　Capacity

　　Impedance

　　Self-disge rate Self-disge rate

　　It is almost impossible to require all the cells in the battery pack to be completely consistent. This means that there will be inconsistent working conditions (internal resistance/heat generation/SOC range) and different aging rates between the cells. Therefore, it is necessary to Balanced management.

　　What are the main tasks of BMS?

　　BMS main tasks:

　　Battery status monitoring

　　Battery status analysis

　　Battery safety protection

　　Energy control management

　　Battery information management

　　…

　　BMS needs to avoid over-range abuse of power batteries and ensure safe, reliable, efficient and long-life operation of power batteries.

　　1. Introduction to BMS system

　　1.1 BMS system architecture

　　A typical BMS system architecture

　　BMS system architecture

　　Master-slave BMS topology

　　Local ECU layer

　　Management of 6-12 cells in a module

　　Communication via CAN or daisy-chain

　　Voltage monitor for every cell

　　Multi-points temperature monitor

　　Passive balance or active balancing

　　Function realization by MCU or ASIC

　　Is daisy chain communication used?

　　Advantages

　　No isolator for each LECU

　　Easy harness for system

　　Low cost

　　Disadvantages

　　EMI/EMC problem for vertical bus

　　Limited range

　　Break on daisy-chain cause the interruption of whole communication

　　Cost comparison of two options

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