In recent years, electric bicycles, hybrid vehicles, electric cars, and fuel cell vehicles powered by lithium batteries have received increasing market attention. The application of power batteries in the transportation sector is of great significance for reducing greenhouse gas emissions, alleviating air pollution, and promoting the development of new energy sources. Lithium batteries, in particular, are gaining increasing attention due to their advantages such as high energy density, high cycle life, light weight, and environmental friendliness. They are already widely used in portable handheld devices such as mobile phones, laptops, and power tools, and are beginning to enter high-power applications such as electric vehicles, becoming a global hotspot in electric vehicle development.
However, lithium batteries are susceptible to shortened lifespan and damage, and may even catch fire or explode, due to abuse conditions such as heating, overcharging/over-discharging current, vibration, and compression. Therefore, safety issues have become a major constraint on the commercialization of power lithium batteries. Developing safety standards and evaluation methods for safe, low-cost, and long-life lithium-ion batteries, controlling the safety and reliability of the battery manufacturing process, and improving battery safety and reliability through the optimal selection of positive and negative electrode materials, electrolytes, and separators are key to ensuring the safety, reliability, and practical application of large-scale power lithium-ion batteries. The battery management system (BMS), as the core component for battery protection and management, must not only ensure the safe and reliable use of the battery but also fully utilize its capabilities and extend its lifespan. As a bridge between the battery, vehicle management system, and driver, the BMS plays an increasingly crucial role in the performance of electric vehicles.
Main functions of battery management system
The battery management system (BMS) is closely integrated with the power battery of an electric vehicle. It continuously monitors the battery's voltage, current, and temperature, and also performs leakage detection, thermal management, battery balancing management, alarm alerts, calculates remaining capacity and discharge power, reports SOC and SOH status, and uses algorithms to control the maximum output power based on the battery's voltage, current, and temperature to achieve the maximum driving range. It also uses algorithms to control the charger to achieve the optimal charging current. The BMS communicates in real time with the vehicle's main controller, motor controller, energy control system, and vehicle display system via a CAN bus interface. Figure 1 shows a simplified block diagram of the battery management system.
The basic functions of a battery management system are: 1) Monitoring the working status of individual battery cells, such as individual battery voltage, operating current, and ambient temperature. 2) Protecting the battery from extreme conditions that could shorten its lifespan, cause damage, or even lead to accidents such as explosions or fires that endanger personal safety.
Generally, a battery management system must have the following circuit protection functions: overvoltage and undervoltage protection, overcurrent and short-circuit protection, over-temperature and over-temperature protection, and multiple protections to improve the reliability of the protection and management system (hardware-executed protection has high reliability, software-executed protection has greater flexibility, and protection against failure of key components in the management system provides a third layer of protection for the user). These functions can meet the needs of most mobile phone batteries, power tools, and electric bicycle applications.
Electric vehicles pose greater challenges to battery management systems.
The electric vehicle battery integrated system is an open power system that communicates via an automotive-grade CAN bus and works in conjunction with the vehicle management system, charger, and motor controller to meet the human-centered safety driving philosophy of automobiles. Therefore, an automotive-grade battery management system must: meet TS16949 and automotive electronics requirements; achieve high-speed data acquisition and high reliability; support automotive-grade CAN bus communication; possess high immunity to electromagnetic interference (the highest level of EMI/EMC requirements); and have online diagnostic functions.
Its main functions are: high-speed acquisition of information such as battery voltage and temperature;
Achieving high-efficiency battery balancing, fully utilizing the capacity of the battery integrated system to improve its lifespan, while reducing heat generation; estimating and displaying battery health and remaining charge; highly reliable communication protocols (automotive-grade CAN communication network); powertrain technology to ensure the battery's full potential, performance, and lifespan under any safe operating conditions; battery temperature and heat dissipation management to ensure the battery system operates in a relatively stable temperature environment; leakage detection and complex grounding design.
Because the battery distribution environment in electric vehicles is very complex, and the batteries operate under high voltage and high power conditions, the requirements for EMI/EMC are very high, which brings greater challenges to the design of battery management systems.
Hierarchical and modular design of electric vehicle battery systems
Because electric vehicle battery systems integrate hundreds or even thousands of battery cells, and considering the space, weight distribution, and safety requirements of the vehicle, these cells are divided into standard battery modules distributed in different locations on the vehicle chassis, and managed uniformly by the powertrain and central processing unit. Each standard battery module also consists of multiple cells connected in parallel and series, managed by the module's electronic control unit. Information from the battery module is reported to the central processing unit and powertrain unit via the CAN bus. After processing this information, the central processing unit and powertrain unit report the final integrated system information, such as remaining charge, health status, and battery capability information, to the vehicle management system via the CAN bus. The hierarchical and modular design of electric vehicle battery systems necessitates a hierarchical and modular design for the battery management system.
Chip integration technology for battery management systems
Automotive battery systems have extremely high reliability requirements, especially the high-voltage monitoring and battery balancing sections. Due to the scarcity of integrated solutions, many solutions rely on discrete components, leading to: poor component matching and reduced signal acquisition accuracy; an increase in external nodes, making automated testing difficult, increasing testing costs, reducing test coverage, and resulting in low system reliability; difficulty in controlling the power consumption of external components; and large system size and high cost.
O2Micro has provided the world's first single-chip solution, the OZ89xx, to support protection and detection of up to five connected battery cells. This solution also supports multi-chip cascading applications. Currently, battery management systems using this chip have been successfully applied in the electronic control units of battery modules for pure electric vehicles and hybrid vehicles.
It is evident that integrated chip solutions play a vital role in improving system reliability and reducing costs, and they are the core of hardware design technology in battery integration.
In the future, lithium-ion batteries have a promising future in the electric vehicle field, and battery management systems will play a crucial bridging role in ensuring safe battery use and communication with vehicle management. Battery management technology encompasses both hardware and software design. High-voltage mixed-signal processing technology and chip design are the core of the hardware design, crucial not only for ensuring high-reliability, high-speed, and high-precision signal acquisition and processing in the automotive environment, but also for improving test coverage, supporting online testing, and reducing costs. The core of the software includes battery management algorithms, communication protocol support, and related powertrain technologies. O2Micro is one of the world's leading suppliers of battery management solutions. Leveraging its years of experience in chip and solution design for battery protection and management, O2Micro has mastered internationally advanced battery management technologies, providing high-quality technical services to global battery manufacturers and system manufacturers, and contributing to the development of electric vehicles in China.
