New design scheme of electric vehicle battery management system

2021-09-11 09:31:22 0

With energy shortages, rising oil prices, and increasingly serious urban environmental pollution, the development and utilization of new energy alternatives to oil is increasingly being valued by governments. In the new energy system, the battery system is an indispensable and important 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. Among them, lithium batteries have attracted more and more attention due to their advantages of high energy density, high repeated cycles, light weight, and 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, and has become a hot spot in the development of global electric vehicles


However, due to the abuse of lithium batteries such as heating, overcharge/overdischarge current, vibration, squeezing, etc., the battery life may be shortened, resulting in damage, and even fire, explosion, etc., so safety issues have become the commercial promotion of power lithium batteries. The main constraints. Safety, low-cost, and long-life lithium-ion battery safety standards, safety evaluation methods, safety and reliability control of the battery manufacturing process, and optimization of positive and negative materials, electrolytes and separators to improve battery safety and reliability are to ensure large-scale power Lithium-ion batteries are safe and reliable, the key to practicality. As the core component of battery protection and management, the battery management system must not only ensure the safe and reliable use of the battery, but also give full play to the capacity of the battery and prolong its service life. It serves as a bridge between the battery and the vehicle management system and the communication between the driver and the battery management system. It plays an increasingly critical 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 all times. At the same time, it also performs leakage detection, thermal management, battery balance management, alarm reminders, calculation of remaining capacity, discharge power, and reporting In the SOC&SOH state, the maximum output power is controlled by the algorithm according to the voltage, current and temperature of the battery to obtain the maximum mileage, and the charger is controlled by the algorithm to charge the best current. Real-time communication with energy control system, vehicle display system, etc. 

The basic functions of the battery management system:

1. Monitor the working conditions of single cells, such as cell voltage, working current, ambient temperature, etc.

2. Protect the battery to avoid battery life shortening, damage, or even explosion, fire and other accidents that endanger personal safety under extreme conditions.


Generally speaking, the battery management system must have the following circuit protection functions: over-voltage and under-voltage protection, over-current and short-circuit protection, over-temperature and over-temperature protection, providing multiple protections for the battery to improve the reliability of the protection and management system (hardware The execution protection has high reliability, the software execution protection has higher flexibility, and the management system key component failure protection provides users with the third protection). These functions can meet the needs of most mobile phone batteries, power tools and electric bicycle applications.

Electric vehicles pose higher challenges to battery management systems


The electric vehicle battery integrated system is an open power system, which communicates through the vehicle-level CAN bus, and works with the vehicle management system, charger, and motor controller to meet the human-oriented safe driving concept of the vehicle. 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 anti-electromagnetic interference capability (the highest level of EMI/EMC requirements), online Diagnostic function.

Its main functions are: high-speed collection of information such as battery voltage and temperature; high-efficiency balance of the battery, full use of the capacity of the battery integrated system to increase the life of the battery integrated system, and reduce heat generation; battery health and remaining power Estimation and display of the battery; high-reliability communication protocol (car-level CAN communication network); powertrain technology must ensure that the battery is used safely under the premise of giving full play to the potential of the battery, ensuring the performance of the battery, and improving the life of the battery; The temperature and heat dissipation management of the battery system is the environmental condition where the temperature is relatively stable; leakage detection and complex grounding design.

Because the distribution environment of batteries in electric vehicles is very complicated, they are in a high-voltage and high-power working state, and require very high EMI/EMC, which brings greater challenges to the design of battery management systems.

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 battery cells are divided into standard battery modules and distributed in different positions on the car chassis , Unified management by the powertrain and the central processing unit; each standard battery module is also composed of multiple cells in parallel and in series, managed by the module's electronic control unit, and reports the battery module information to the central processing unit through the CAN bus After processing this information, the final information about the integrated system, such as remaining power, health status, and battery capacity-related information, are reported to the vehicle management through the CAN bus. system. The hierarchical and modular design of electric vehicle battery systems requires the hierarchical design of battery management systems

Chip integration technology of battery management system

The reliability requirements of automobile battery systems are extremely high, especially the high-voltage monitoring part and the battery equalization part. Because there are few integrated solutions, many solutions are made up of discrete components, resulting in poor component matching and reduced signal acquisition accuracy; The increase in external nodes makes 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 solution OZ89xx that supports single-chip protection and detection of >5 batteries connected in series. The solution also supports multi-chip cascading applications. At present, the battery management system solution using this chip has been successfully used in the battery module electronic control unit of pure electric vehicles and hybrid electric vehicles.

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

In the future, power lithium batteries have broad prospects in the field of electric vehicles, and the battery management system will play a key role as a bridge for 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. It is not only the key to ensuring high reliability, high speed, and high precision signal acquisition and processing in the automotive environment, but also The key to improving test coverage, supporting online testing, 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 major battery management solution suppliers. With years of experience in battery protection and management in chip design and solution design, O2Micro has mastered the international advanced level of battery management technology to provide global battery manufacturers and system manufacturers With high-quality technical services, it has contributed its own strength to the development of China's electric vehicles.