With the shortage of energy, rising oil prices, and increasingly serious urban environmental pollution, the development and utilization of new energy alternatives to petroleum is increasingly valued by governments. In the new energy system, the battery system is an indispensable part of it. In recent years, electric bicycles, hybrid vehicles, electric vehicles, and fuel cell vehicles powered by lithium batteries have received more and more attention from the market. The application of power batteries in the transportation field is of great significance for reducing greenhouse gas emissions, reducing air pollution and the application of new energy sources. Lithium batteries have attracted more and more attention due to their high energy density, high repetition rate, light weight and green environmental protection. Therefore, they have been widely used in portable handheld devices such as mobile phones, notebook computers and power tools. Has begun to enter high-power applications such as electric vehicles and electric vehicles, becoming a hot spot in the development of electric vehicles worldwide.
However, due to the heating, overcharge/over-discharge current, vibration, extrusion and other abuse conditions, the lithium battery may cause the battery life to be shortened and damage, and even fire, explosion and other events may occur. Therefore, the safety problem becomes a commercialization of the power lithium battery. The main constraints. Safe, low-cost, long-life lithium-ion battery safety standards, safety evaluation methods, safety and reliability control of battery manufacturing processes, and optimization of battery safety and reliability through positive and negative materials, electrolytes and diaphragms to ensure large power The key to safe, reliable and practical lithium-ion batteries. As the core component of battery protection and management, the battery management system not only needs to ensure the safe and reliable use of the battery, but also to fully utilize the battery capacity and extend the service life. As a bridge between the battery and the vehicle management system and the driver, the battery management system It plays an increasingly important role in the performance of electric vehicles.
Main functions of the battery management system
The battery management system is closely integrated with the power battery of the electric vehicle to detect the voltage, current and temperature of the battery at the same time. At the same time, it also conducts leakage detection, thermal management, battery balance management, alarm reminder, calculation of remaining capacity, discharge power, and report. SOC&SOH state, according to the voltage, current and temperature of the battery, the maximum output power is controlled by algorithm to obtain the maximum mileage, and the optimal current is charged by the algorithm to control the charger. The CAN bus interface and the onboard controller, motor controller, Real-time communication is performed by an energy control system, an in-vehicle display system, and the like. Figure 1 is a simplified block diagram of a battery management system.
The basic functions of the battery management system: 1) monitor the working condition of the single cell, such as cell voltage, operating current, ambient temperature, etc. 2) Protect the battery to avoid battery life under extreme conditions, such as shortened battery life, damage, and even accidents such as explosions and fires that endanger personal safety.
In general, battery management systems must have the following circuit protection features: overvoltage and undervoltage protection, overcurrent and short circuit protection, over- and over-temperature protection, multiple protections for the battery to improve protection and manage system reliability (hardware The protection performed is highly reliable, the protection of software execution is more flexible, and the protection of critical components of the management system provides the user with a third protection). These features meet the needs of most mobile phone batteries , power tools and electric bicycle applications.
Electric vehicles pose a higher challenge to battery management systems
The electric vehicle battery integrated system is an open power system that communicates through the automotive-grade CAN bus and works in conjunction with the vehicle management system, charger, and motor controller to meet the car-oriented safe driving concept. Therefore, the automotive battery management system must: meet the requirements of TS16949 and automotive electronics, achieve high-speed data acquisition and high reliability, automotive-grade CAN bus communication, high immunity to electromagnetic interference (the highest level of EMI / EMC requirements), online Diagnostic function.
Its main function is: high-speed acquisition of information such as battery voltage and temperature;
Achieve high efficiency and balanced battery, fully utilize the capacity of the battery integrated system to improve the life of the battery integrated system, while reducing heat generation; battery health and residual power estimation and display; high reliability communication protocol (automobile level CAN communication) Network); powertrain technology to ensure the safe use of the battery, give full play to the potential of the battery, ensure the performance of the battery, improve the battery life; battery temperature and heat management, the battery system works at a relatively stable temperature Environmental conditions; leakage detection and complex ground design.
Since the distribution environment of the battery in the electric vehicle is very complicated, the working condition of high voltage and high power has very high requirements for EMI/EMC, which brings greater challenges to the design of the battery management system.
Hierarchical and modular design of electric vehicle battery system
Since the electric vehicle battery system is integrated by hundreds of battery cells, considering the space, weight distribution and safety requirements of the car, these cell units are divided into standard battery modules, which are distributed in different positions on the chassis of the car. It is managed by the powertrain and the central processing unit; each standard battery module also has multiple batteries composed of parallel and series, which is managed by the electronic control unit of the module, and reports the information of the battery module to the central processing through the CAN bus. And the powertrain unit, the central processing unit and the powertrain unit process the information, and then report the final information about the integrated system, such as remaining power, health status, and battery capability information, to the vehicle management via the CAN bus. system. The hierarchical and modular design of the electric vehicle battery system requires the hierarchical and modular design of the battery management system.
Chip integration technology for battery management systems
The reliability requirements of automotive battery systems are extremely high, especially for high-voltage monitoring and battery balancing. Due to the lack of integrated solutions, many solutions are made up of discrete components, resulting in poor component matching and reduced signal acquisition accuracy. The number of external nodes increases, making it difficult to automate testing, increasing test costs, reducing test coverage, and low system reliability; the power consumption of external components is difficult to control; the system size is large and the cost is high.
O2Micro provides the world's first OZ89xx solution that supports five-cell serial tandem protection and detection. The solution also supports multi-chip cascading applications. At present, the battery management system solution using the chip has been successfully used in the electric control unit of the pure electric vehicle and the hybrid vehicle battery module.
It can be seen that the integrated chip solution plays an important role in improving system reliability and reducing cost. He is the core of hardware design technology in battery integration technology.
In the future, power lithium batteries have broad prospects in the field of electric vehicles, and battery management systems 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, and high-voltage mixed-signal processing technology and chip design are the core of hardware design, which is not only the key to ensure high-reliability, high-speed, high-precision signal acquisition and processing in the automotive environment. The key to improving test coverage, supporting online detection and reducing costs; the core of the software includes battery management algorithms, communication protocol support, and powertrain related technologies. O2Micro is one of the world's leading suppliers of battery management solutions. With its years of experience in chip design and design for battery protection and management, O2Micro has mastered the internationally advanced battery management technology for global battery manufacturers. System manufacturers have provided high-quality technical services and contributed their own strength to the development of electric vehicles in China.
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