With the energy shortage, oil price rise and urban environmental pollution becoming more and more serious, the development and utilization of new energy instead of oil has been paid more and more attention by the governments of all countries. In the new energy system, the battery system is an indispensable 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. Of lithium battery with high energy density and high repetition cycle use, light weight, and the advantages of the green environmental protection more and more get the attention of people, so in mobile phones, laptops, electric tools and so on have been widely used in portable handheld devices, and has begun to enter the electric vehicles, electric vehicles and other high power applications, is becoming a hot spot of global electric car development.

However, due to the abuse of heating, overcharge/overdischarge current, vibration, extrusion and other conditions, the battery life may be shortened and damaged, and even occur fire, explosion and other events, so the safety issue has become the main restriction factor for the commercial promotion of power lithium battery. Safety standards, safety evaluation methods, safety and reliability control of battery manufacturing process, and improvement of battery safety and reliability through anode and anode materials, electrolyte and membrane optimization are the keys to ensure the safety, reliability and practicality of large power lithium ion batteries. As the battery and battery management system as the core parts of the conservation and management not only to ensure the battery safe and reliable use, and to give full play to their ability and prolong the service life of the battery, as the battery and vehicle management system as well as the bridge of the driver, battery management system for electric vehicle is playing a more and more crucial role in performance.

The main functions of the battery management system

The battery management system is closely integrated with the power battery of electric vehicles, which can detect the voltage, current and temperature of the battery at any time, and also carry out leakage detection, thermal management, battery balance management, alarm reminder, calculate the remaining capacity and discharge power, and report the SOC&SOH status. According to the voltage, current and temperature of the battery, the maximum output power is controlled by the algorithm to obtain the maximum driving range, and the algorithm is used to control the charger to charge the best current. Through the CAN bus interface, real-time communication is carried out with the on-board total controller, the motor controller, the energy control system and the on-board display system. Figure 1 is a simple block diagram of a battery management system.

The basic functions of the battery management system are as follows: 1) Monitor the working conditions of the single cell, such as the voltage of the single cell, the working current, the ambient temperature, etc. 2) Protect the battery to avoid the battery life shortening, damage, or even explosion, fire and other accidents endangering personal safety when the battery works under extreme conditions.

In general, the battery management system must have the following circuit protection features: Over-voltage and under-voltage protection, over current and short circuit protection, high moderate low temperature protection, for the battery to provide multiple protection to improve the reliability of the protection and management system, the protection of the hardware to perform with high reliability, the protection of the software implementation has higher flexibility, management system of key components failure to provide users with the protection of the third heavy protection). These features will suffice for most mobile phone batteries, power tools, and e-bike applications.

Electric vehicles pose an even greater challenge to battery management systems

Electric vehicle battery integrated system (EV) is an open power system, which communicates through the auto-level CAN bus and works in coordination with 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 CAN bus communication, high anti-electromagnetic interference ability (the highest level of EMI/EMC requirements), online diagnosis function.

Its main functions are as follows: high-speed collection of battery voltage and temperature information;

Realize the high efficiency balance of the battery, give full play to the capacity of the battery integrated system so as to improve the life of the battery integrated system, while reducing the heat generation; Estimation and display of battery health and remaining power; Highly reliable communication protocol (automotive CAN communication network); Powertrain technology to ensure any safe use of the battery, give full play to the potential of the battery, ensure the performance of the battery, improve the life of the battery; The temperature and heat dissipation management of the battery is that the battery system works in a relatively stable temperature environment. Leakage detection and complex ground wire design.

Due to the very complex distribution environment of batteries in electric vehicles and the high voltage and large power working state, 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

Since the electric vehicle battery system is composed of hundreds of cells integrated, considering the space, weight distribution and safety requirements of the vehicle, these cells are divided into standard battery modules, distributed in different locations of the vehicle chassis, by the power train and central processing unit unified management; Each standard battery module is composed of multiple batteries in parallel and series, which is managed by the module's electronic control unit. The information of the battery module is reported to the central processor and powertrain unit through CAN bus, and the central processor and powertrain unit process the information. The final information related to the integrated system, such as residual power, health status and battery capability, is reported to the vehicle management system via the CAN bus. The hierarchical and modular design of the battery system of electric vehicles requires the hierarchical and modular design of the battery management system.

Chip integration technology for battery management system

The reliability requirements of automobile battery system are very high, especially for the high-voltage monitoring part and the battery balance part. Because there are few integrated solutions, many of them are made of discrete components, which leads to: the component matching degree is not good, and the precision of signal acquisition is decreased; External nodes increase, it is difficult to achieve automated testing, improve test costs, reduce test coverage, 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 support for "5-cell series single chip protection and detection solution OZ89XX, the solution also supports multi-chip cascading applications. At present, the scheme of battery management system using this chip has been successfully used in battery module ECU of pure electric vehicle and hybrid vehicle.

Therefore, 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 a broad prospect in the field of electric vehicles, and the battery management system will play a key role in the safe use of batteries and communication with vehicle management. Battery management technology, including hardware design and software design technology, and the high pressure mixed signal processing technology and chip design is the core of hardware design, not only is the guarantee in the automotive environment to achieve high reliability, high speed, high precision signal acquisition and processing of the key, and improve the test coverage, support on-line detection and reduce the cost of key; The core of the software includes the algorithm of battery management, the support of communication protocol and the related technology of powertrain. Concave and convex technology (O2Micro) is one of the world's main battery management solutions provider, with its protection and the battery management chip design and design experience for many years, has mastered the international advanced battery management technology, for the global battery manufacturers, system manufacturers to provide high quality technical service, contributing to the development of China's electric power of its own.