Design of a new lithium-ion battery management system
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2023/08/26 15:19:11
Battery conduction system (Management system,BMS), which includes technology and microcomputer detection, performs dynamic monitoring of the battery cell and battery operation conditions, can accurately check the remaining battery capacity, battery charge and discharge maintenance, the best operating conditions, the decline of working capital, and service life. In this paper, a new lithium-ion battery management system is designed and implemented by synthesizing some advanced technical achievements at home and abroad. The management architecture adopts modular and distributed planning, and the system includes a secondary control structure, namely a local measurement module and a central processing module. During this period, the important function of the central processing module is to communicate with the host computer through the RS232 interface and connect with the local measurement module through the CAN bus network method. The important functions of the local measurement module are data acquisition (mainly for temperature, current and voltage data acquisition), charge and discharge control, power measurement, single cell 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 this battery management system should complete the following functions:
1) Collect battery information in real time, including the total voltage of battery pack, voltage of single battery, charging and discharging current, temperature and other parameters; 2) Remaining power measurement and display;
3) CAN supply data transmission interface, complete communication with CAN bus and host computer; 4) Good human-computer interaction, safe and reliable system, strong anti-interference ability.
2. Plan the hardware of the local measurement module
2.1 Voltage acquisition module
Single battery terminal voltage is an important basis for calculating the remaining battery, the choice of charge and discharge mode, and the evaluation of the operating state, so the premise of monitoring the battery pack is to have a reasonable measurement method of single battery terminal voltage. However, due to the large number of batteries in the battery pack, the total voltage is high, and the measurement accuracy is high, 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 charge, and achieves the purpose, the capacitor voltage is the same as the battery voltage; The second step is to disconnect the multiple switches kn-1 and kn-2 controlled by the MCU, turn off the K1 and K2 switches, and connect them to the A/D module of the MCU for measurement. When measuring the time, according to the consideration of preventing the influence of the battery terminal voltage instability, the module chooses the method of average 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 the actual circuit, a relay can be used to complete the analog switch.
2.2 Current Acquisition module
For the measurement of dynamic current in charge and discharge process, ltsr25-np current sensor of LEM company is used in this paper. The device is a closed-loop multi-range current sensor which compensates according to the Hall effect and adopts the unipolar voltage method. It has the advantages of high measurement accuracy, no insertion loss, good linearity, strong current overload ability and so on. The measurement accuracy can reach ±0.2% below 25℃. The rated current is 25 amps and the maximum measurable current is 80 amps. The current sensor can convert the charge and discharge 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 charge and discharge current.
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