Design of battery management system for the hottes

Design of battery management system for electric vehicles

with the shortage of energy, the rising price of oil, and the increasingly serious urban environmental pollution, the development and utilization of new energy sources that replace oil have been paid more and more attention by governments all over the world. In the new energy system, battery system is an indispensable and important part. In recent years, electric bicycles, hybrid electric vehicles, electric vehicles and fuel cell vehicles powered by lithium batteries have attracted more and more attention in the market. The application of power batteries in the field of transportation is of great significance for reducing greenhouse gas emissions, reducing air pollution and the application of new energy. Among them, lithium batteries have attracted more and more attention because of their high energy density, high number of repeated cycles, light weight, green environmental protection and other advantages. Therefore, lithium batteries have been widely used in portable handheld devices such as, notebook computers, electric tools and so on, and have begun to enter high-power applications such as electric vehicles and electric vehicles, and have become a hot spot in the development of electric vehicles worldwide

but because lithium batteries are heating Overcharge/discharge current, vibration, extrusion and other abuse conditions may lead to battery life shortening and damage. Even polyether ether ketone (PEEK), as a new medical implant material, will cause fire, explosion and other events. Therefore, the safety problem has become the main constraint to the commercialization and promotion of power lithium batteries. Don't you know the safety standards, safety evaluation methods, safety and reliability control of battery manufacturing process and the positive and negative materials and electrolytes of safe, low-cost and long-life lithium-ion batteries? And diaphragm optimization to improve the safety and reliability of batteries is the key to ensure the safety, reliability and practicality of large power lithium-ion batteries. As the core component of battery protection and management, the battery management system should not only ensure the safe and reliable use of the battery, but also give full play to the ability of the battery and prolong the service life. As a bridge between the battery and the vehicle management system and the driver, the battery management system plays an increasingly critical role in the performance of electric vehicles

the main functions of the battery management system

the battery management system is closely combined with the power battery of electric vehicles to detect the voltage, current and temperature of the battery at all times. At the same time, it also carries out leakage detection, thermal management, battery balance management, alarm reminder, calculate the residual capacity and discharge power, and report the soc&soh status, According to the voltage, current and temperature of the battery, the algorithm is used to control the maximum output power to obtain the maximum mileage, and the algorithm is used to control the charger to charge the best current. Real time communication is carried out with the on-board general controller, motor controller, energy control system, vehicle display system, etc. through the CAN bus interface. Figure 1 is a simple block diagram of the battery management system

Figure 1: a simple block diagram of the battery management system

basic functions of the battery management system: 1) monitor the working conditions of individual cells, such as battery voltage, working current, ambient temperature, etc. 2) Protect the battery and avoid battery life shortening, damage, explosion, fire and other accidents endangering personal safety under extreme conditions

generally speaking, the battery management system must have the following circuit protection functions: overvoltage and undervoltage protection, overcurrent and short circuit protection, over high temperature and low temperature protection, and provide multiple protection for the battery to improve the reliability of the protection and management system (the protection executed by hardware has high reliability, the protection executed by software has higher flexibility, and the protection against the failure of key components of the management system provides the third level of protection for users). These functions can meet the needs of most battery, electric tool and electric bicycle applications

electric vehicles pose a higher challenge to the battery management system

the battery integrated system of electric vehicles is an open power system, which communicates through the automobile level can bus and works with the guide pipe of the automatic feeding turntable connected with the vehicle management system, charger and motor controller, so as to meet the car's people-oriented safe driving concept of wiping and oiling when not in use. Therefore, the automotive battery management system must meet the requirements of TS16949 and automotive electronics, realize high-speed data acquisition and high reliability, automotive can bus communication, high anti electromagnetic interference ability (the highest emi/emc requirements), and diagnostic function

its main functions are: high-speed collection of battery voltage, temperature and other information; Achieve high efficiency and balance of the battery, give full play to the capacity of the battery integrated system, so as to improve the service life of the battery integrated system and reduce the generation of heat at the same time; Estimation and display of battery health and remaining power; Highly reliable communication protocol (Automotive can communication network); Powertrain technology should give full play to the potential of the battery, ensure the performance of the battery and improve the service life of the battery on the premise of ensuring any safe use of the battery; The temperature and heat dissipation management of the battery is the environmental condition in which the battery system works at a relatively stable temperature; Leakage detection and complex ground wire design

due to the complex distribution environment of batteries in electric vehicles, which are in the working state of high voltage and high power, the requirements for emi/emc are very high, which brings greater challenges to the design of battery management system

hierarchical and modular design of electric vehicle battery system

because the electric vehicle battery system is integrated by hundreds of cell units, considering the space, weight distribution and safety requirements of the vehicle, these cell units are divided into standard battery modules, distributed in different positions of the vehicle chassis, and managed by the powertrain and Central processing unit; Each standard battery module is also composed of multiple cells in parallel and in series, which are managed by the electronic control unit of the module. The information of the battery module is reported to the central processing unit and powertrain unit through the CAN bus. After these information are processed, the central processing unit and powertrain unit send the final information about the integrated system, such as residual power Health status and battery capacity related information are reported to the vehicle management system through the CAN bus. The hierarchical and modular design of electric vehicle battery system requires the hierarchical and modular design of battery management system (Figure 2)

Figure 2: hierarchical and modular design of electric vehicle battery management system

chip integration technology of battery management system

the reliability requirements of automotive battery system are very high, especially the high-voltage monitoring part and battery balancing part. Because there are few integrated solutions, many solutions are made of discrete components, resulting in poor component matching and reduced accuracy of signal acquisition; With the increase of external nodes, it is difficult to achieve automated testing, improve the testing cost, reduce the testing coverage, and the system reliability is low; The power consumption of external components is difficult to control; The system is large in size and high in cost

bump technology (O2micro) provides the world's first program oz89xx that supports the protection and detection of>5 batteries connected in series on a single chip. This program also supports the application of multi chip cascading. At present, the battery management system scheme using this chip has been successfully used in the battery module electronic control unit of pure electric vehicles and hybrid electric vehicles. Table 1 takes the standard battery module as an example to introduce the comparison between the discrete scheme and the integrated scheme

it can be seen that the solution of integrated chip plays a very important role in improving the reliability of the system and reducing the cost. It is the core of hardware design technology in battery integration technology

summary of this paper

in the future, power lithium batteries have broad prospects in the field of electric vehicles, and battery management system will play a key role in the safe use of batteries and communication with vehicle management. Battery management technology includes hardware design technology and software design technology. Among them, high-voltage mixed signal processing technology and chip design are the core of hardware design. They are not only the key to ensure high-reliability, high-speed and high-precision signal acquisition and processing in the automotive environment, but also the key to improve test coverage, support detection and reduce costs; The core of the software includes battery management algorithm, communication protocol support and powertrain related technology. O2micro is one of the major suppliers of battery management solutions in the world. With its many years of experience in chip design and scheme design in battery protection and management, it has mastered the internationally advanced battery management technology, provided high-quality technical services for global battery manufacturers and system manufacturers, and contributed its own strength to the development of electric vehicles in China