Design of a new lithium ion battery management system
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2023/03/28 11:39:14
Battery conduction system (management system,BMS), it includes technical and microcomputer detection, perform dynamic monitoring of the battery unit and battery operation conditions, can accurately check the remaining capacity of the battery, battery charging and discharging maintenance, the best operating conditions, working capital decline, service life. In this paper, a new lithium ion battery management system is designed and implemented based on some advanced technological achievements at home and abroad. The management architecture adopts modular and distributed planning, and the system includes two level control structure, namely the local measurement module and the central processing module. During this period, the important function of the central processing module is to communicate with the upper computer through RS232 interface, and connect with the local measurement module through CAN bus network method. The important functions of the local measurement module are data acquisition (mainly used for temperature, current and voltage data acquisition), charge and discharge control, power measurement, single battery balance and communication with the central processing module using CAN bus technology.
1. Plan the system hardware
The battery processing system planned in this paper is mainly used in electric vehicles and some underwater equipment, so the system planning should be reasonable in structure, advanced in technology and strong in scalability. The technical precision of each parameter of the system is higher. Therefore, the planning of the battery management system should complete the following functions:
1) Real-time collection of battery information, including total voltage of battery pack, voltage of single battery, charging and discharging current, temperature and other parameters; 2) Measurement and display of residual electricity;
3) Data transmission interface CAN be supplied to complete the communication with CAN bus and upper computer; 4) Good man-machine interaction, safe and reliable system, strong anti-interference ability.
2. Plan the hardware of the local measurement module
2.1 Voltage acquisition module
The terminal voltage of single battery is an important basis for the calculation of the remaining battery, the choice of charging and discharging mode, and the evaluation of the running state, so the premise of monitoring the battery pack is to have a reasonable measurement method of the terminal voltage of single battery. However, due to the large number of batteries in the battery pack and the high total voltage, the measurement accuracy is required, so it is difficult to achieve power measurement. The working principle of the voltage monitoring plan is as follows: the first step, the single-chip microcomputer controls the multi-channel switch kn-1 and kn-2(the number between n1 and 7), synchronously connects the capacitors at both ends of the corresponding battery, starts the capacitor charging, and achieves the goal, the capacitor voltage is the same as the battery voltage; The second step is to disconnect the kn-1 and kn-2 multiplex switches controlled by MCU, turn off the K1 and K2 switches, and connect them to the A/D module of MCU for measurement. When measuring time, in order to avoid the influence of battery terminal voltage instability, the module chooses the method of average value measurement. This method can easily use the A/D unit inside the microprocessor, without adding A/D module rating, improve planning efficiency and save money. Usually in a real circuit, a relay can be used to complete the analog switch.
2.2 Current Acquisition module
In this paper, ltsr25-np current sensor of LEM company is used to measure dynamic current in charge and discharge process. The device is a closed - loop multi - range current sensor which compensates according to Hall effect and uses the single pole voltage method. It has the advantages of high measurement accuracy, no insertion loss, good linearity and strong current overload ability. The measuring accuracy can reach ±0.2% below 25℃. The rated current is 25 amps and the maximum measured current is 80 amps. The current sensor can convert the charging and discharging current into A voltage signal of 0~5 volts, and then connect to the A/D unit of the single chip microcomputer to measure the charging and discharging current.
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