As far as the scope of battery management is concerned, it can be discussed in both broad and narrow sense. The generalized battery management can involve the charging and load discharging of the battery, with the purpose of improving the performance of the battery, coordinating charging and discharging, and adjusting the charging and discharging speed under appropriate circumstances, which is equivalent to the power management and energy management part of a system. A typical application is battery management for hybrid vehicles. Since the energy supply of hybrid electric vehicles is not only the battery, but also other energy sources, the charging and discharging speed of the battery and the ratio of energy supply can be arranged according to the actual situation of the battery. In a narrow sense, Artemisia battery management only manages the various states and parameters of the battery, and provides necessary data communication and other functions, and does not involve charge management and discharge management. This is also more in line with the term “battery management”.
The charging of the battery is limited by the power supply capacity and voltage of the charger (machine), which is an extension of battery management and is not controlled by the battery management; similarly, the discharge of the battery is mainly affected by the size of the load, and the adjustment of the load size is generally at a higher level The management level of the battery is not adjusted by the battery management according to the battery’s own conditions. The battery management only monitors the battery status and the state of charge in the battery, and makes appropriate control adjustments to the battery and its internal components according to its status. The battery management does not control other components outside the battery, but only provides the communication data status notification function. But the battery management receives the control information of the upper main control module and makes the necessary control response. At present, the battery management system in the general sense refers to the narrowly-defined concept of battery management. The charging management is realized by the charger (machine), and its interface is generally realized by the battery voltage. The charger uses the battery voltage to determine whether to use constant current charging/constant voltage charging, current dissipation charging, floating charging, etc. Discharge management and load management are managed by the upper main control module of the battery to make necessary adjustments according to the information provided by the battery management.
As an important part of electric vehicles, the electric vehicle battery management system has important functions such as real-time monitoring of battery status, optimizing the use of battery energy, extending battery life and ensuring the safety of the battery. The battery management system has a great influence on the safe operation of the entire electric vehicle, the choice of vehicle control strategy, the choice of charging mode, and the operating cost. The battery management system must reliably complete the real-time monitoring and fault diagnosis of the battery status both during the operation of the vehicle and during the charging process, and inform the vehicle integrated controller or charger through the bus, so as to adopt a more reasonable control strategy. To achieve the purpose of effective and efficient use of batteries.
The battery management system is closely integrated with the battery to detect the voltage, current, and temperature of the battery in real time. At the same time, it also performs leakage detection, thermal management, battery equalization management, alarm reminders, calculation of remaining capacity, discharge power, and reporting of SOC and SOH status. It also uses algorithms to control the maximum output power according to the voltage, current and temperature of the battery to obtain the maximum mileage, and uses the algorithm to control the charger to charge the battery with the best current. Energy control system, vehicle display system, etc. carry out real-time communication.
The power battery management system is indispensable in the battery charging process. The main function of the battery management system is to monitor the voltage and temperature of each single battery and the current of the battery pack in real time during the charging process of the battery pack, after processing and comparison, output alarm and control information, and display the battery pack and each cell Real-time and historical information of the battery. The battery management system is an important guarantee for the best and safe charging of the battery.
The battery pack is prone to problems during the charging process, mainly caused by the excessive consistency error of the battery. For this reason, in the past ten years, many experts and scholars at home and abroad, manufacturers and users of batteries have vigorously carried out research aimed at solving the harm caused by battery consistency errors, and developed various In order to meet the requirements of battery balancing, the battery management system has developed balancing methods such as shunt method, cut-off method, parallel method, energy recovery method, auxiliary charging method, single charging method, etc.
But from the theoretical analysis and actual use effect, there are few satisfactory results. This is not because of problems with electronic technology, but because of problems with the concept of battery management systems and battery management strategies. For this reason, the battery management system must be designed in accordance with scientific concepts and effective strategies. The recommended method is to monitor the voltage, temperature and battery current of each battery in real time during charging, discharging and parking, and set the highest charging voltage, lowest discharging voltage, highest and The threshold value of the minimum operating temperature and maximum current. When the voltage, temperature, and battery current of a certain battery exceed the limit, the regulation and alarm function will be activated. On the one hand, it is guaranteed that any single battery will not work beyond the limit. On the other hand, it is guaranteed to continue charging at a slightly smaller charging current until the charging ends when the total charging voltage and the minimum charging current reach the set value, and the equalizing charging of the battery is automatically carried out during the regulated charging process.
At present, the main factors affecting the popularization and application of electric vehicles include the safety and use cost of power storage batteries. Extending the service life of storage batteries is one of the effective ways to reduce use costs. In order to ensure the good performance of the battery and prolong the service life of the battery, the battery must be managed and controlled reasonably and effectively. The battery management system can monitor the condition of the power battery in real time to ensure the normal operation of electric vehicles.
Both at home and abroad have invested a lot of manpower and material resources to carry out extensive and in-depth research on battery management systems. Japan’s Aomori Industrial Research Center has continued to conduct research on the practical application of battery management systems since 1997; Vi11anova University in the United States and US Nanocorp have cooperated for many years to conduct fuzzy logic-based analysis of various types of battery SOC (battery remaining power). Forecast: Toyota, Honda, and General Motors have all put battery management systems into the focus of technology development. During the Tenth Five-Year Plan period, my country set up major special research projects for electric vehicles, actively promoted the research, development and engineering application of battery management systems, and achieved a series of results and breakthroughs.
Compared with motors, motor control technology, and battery technology, the battery management system is not very mature. As one of the most critical technologies for electric vehicles, battery management system has been greatly improved in recent years. Many aspects have entered the practical application stage, but some parts are still not perfect, especially in the reliability of collected data and SOC estimation. Accuracy and safety management need to be further improved and improved.
The battery management system must reliably complete the real-time monitoring and fault diagnosis of the battery status during the operation of the vehicle or during the charging process, and inform the electric vehicle controller or charger through the bus to adopt a more reasonable control strategy. To achieve the purpose of effective and efficient use of batteries. The battery management system adopts a distributed system structure. Each battery management system consists of a central control module (or master) and 10 battery measurement and control modules (or slaves). The battery management system detection module is installed in the front panel of the battery box, and the battery management system main control module is installed in the high-voltage equipment compartment at the rear of the vehicle. The functions of the battery management system are as follows:
(1) Detection function, including single battery voltage detection, temperature detection, battery pack operating current detection, insulation resistance detection, etc.
(2) Dynamic detection function, which dynamically detects the insulation resistance between the power battery and the chassis of the vehicle, and can display the change process of the insulation resistance on the panel.
(3) Estimation function of battery pack SOC.
(4) Cooling fan control function.
(5) Recording function, including record of charge and discharge times, record of charge and discharge times of single battery, etc.
(6) Evaluation of discreteness of single-box storage battery.
(7) Communication function, including communication with on-board equipment, providing necessary battery data (CANI) for vehicle control; communicating with on-board monitoring equipment, sending battery information to the panel display (CAN2); communicating with chargers to safely realize battery Charging (CAN3).
(8) The battery balance maintenance function detects the temperature difference between single batteries, and reaches a certain temperature difference, and gives instructions to perform battery balance maintenance.
(9) Initialization function. The battery management system can be initialized by simple equipment, which can meet the needs of quick battery replacement and regrouping of battery boxes.
(10) Fault detection and alarm function, including battery fault analysis and online alarm, battery management system self-check and processing, when the battery management system fails, the system can perform self-check, control according to battery pack requirements, and deal with it accordingly .
(11) The basic protection functions of the battery management system include:
① Overvoltage protection function (OV). When charging (including braking energy recovery), when the charging voltage of any battery exceeds the set value, the charging voltage is automatically reduced to prevent the battery from overcharging.
②) Low-voltage protection function (UV). When discharging, when the discharge voltage of any battery is lower than the set value, the discharge will be stopped to prevent the battery from over-discharging.
③High temperature protection function (OT), whether it is charging or discharging or parking sleep state, when the temperature of any battery exceeds the set value, the battery thermal management system is activated to reduce the battery temperature. When the maximum allowable temperature is exceeded, the circuit should be automatically cut off immediately.
④ Low temperature protection function (UT), when charging, when the battery temperature is lower than the set value, the automatic change of the charging current is generally reduced to 1/3 of the charging current; when discharging, when the battery temperature is lower than the set value, start The battery thermal management system improves the battery temperature.
⑤ Overcurrent protection function (OC). When charging and discharging, the current of the battery exceeds the set value, and the current increase is automatically limited.
⑥ Short circuit protection function (SC). When charging, discharging, and parking dormant state, when the battery is short-circuited, the circuit will be automatically cut off.