Designed and implemented a new lithium-ion battery management system
Battery conduction system (management system, BMS), which includes technology and microcomputer detection, performs dynamic monitoring of battery cells and battery operation conditions, can accurately check the remaining battery capacity, battery charging and discharging maintenance, and working capital under the best operating conditions The decline in service life. This article has synthesized some advanced technical achievements at home and abroad, designed and realized a new type of lithium-ion battery management system. The management structure adopts modular and distributed planning, and the system includes two-level control structure, namely local measurement module and 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 to connect with the local measurement module through the CAN bus network method. The important functions of the local measurement module are data acquisition (importantly used for temperature, current and voltage data acquisition), charge and discharge control, power measurement, single cell balance, and use CAN bus technology to communicate with the central processing module.
1. System hardware planning
The battery processing system planned in this article is mainly applied to electric vehicles and some underwater equipment, so the system planning should have a reasonable structure, advanced technology, and strong scalability; the technical accuracy of the system parameters is high. Therefore, the planning of this battery management system should complete the following functions:
1) Collect battery information in real time, including parameters such as total battery voltage, single battery voltage, charge and discharge current, temperature, etc.;
2) Measurement and display of remaining power;
3) Data transmission interface can be supplied to complete the communication with CAN bus and upper computer;
4) Good human-computer interaction, safe and reliable system, and strong anti-interference ability.
2. Hardware planning of local measurement module
2.1 Voltage acquisition module
The terminal voltage of the single battery is an important basis for calculating the remaining battery, the selection of charging and discharging methods, and the evaluation of the running state, so the premise of monitoring the battery pack is to have a reasonable method for measuring the voltage of the single battery. However, due to the large number of batteries in the battery pack, the high total voltage, and high measurement accuracy requirements, it is difficult to achieve power measurement. The working principle of the voltage monitoring plan is as follows: In the first step, the single-chip microcomputer controls the multi-channel switches kn-1 and kn-2 (numbers between n1 and 7), synchronously connect the capacitors at both ends of the corresponding battery, start the capacitor charging, and achieve the purpose , The capacitor voltage is the same battery voltage; the second step is to disconnect the kn-1 and kn-2 multiplexers controlled by the MCU, close the K1 and K2 switches, and connect them to the A/D module of the MCU for measurement. When measuring time, the module chose the method of average value measurement based on the consideration of preventing the effect of the unstable battery terminal voltage. This method can easily use the A/D unit inside the microprocessor without adding A/D module rating, improving planning efficiency and saving money. Usually in the actual circuit, a relay can be used to complete the analog switch.
2.2 Current acquisition module
Regarding the measurement of dynamic current during charging and discharging, this article uses LEM's ltsr25-np current sensor. This element is a closed-loop multi-range current sensor, which is compensated according to the Hall effect and adopts the unipolar voltage method. It has the advantages of high measurement accuracy, no insertion loss, good linearity, and strong current overload capability. The measurement accuracy can reach ±0.2% below 25℃. The rated current is 25 amperes, and the maximum measurable current is 80 amperes. The current sensor can convert the charge and discharge current into a voltage signal of 0 to 5 volts, and then connect it to the A/D unit of the microcontroller to measure the charge and discharge current.
Lithium-ion battery material technology
Technical characteristics and development trends of lithium-ion battery materials
The lithium-ion battery industry requires the integration of multiple technologies, including electrochemical technology, production technology, electronic technology, and material development technology. Lithium-ion batteries should not only continue to develop theoretically, but also have correspondingly high production requirements. They must rely on excellent equipment and factory conditions and high-quality technical workers to be able to produce qualified lithium-ion batteries. The following editor will introduce the technical characteristics of Xianyi.com and the technological development trend of lithium-ion battery materials.
From the technical barriers of raw materials, lithium ion battery professional technology separator> anode material> electrolyte> anode material. But now the central problem that always prevents the use of lithium-ion battery industrialization strategies is anode materials.On the one hand, the anode material of lithium-ion batteries has the highest capital, reducing the source of anode materials for lithium-ion batteries, and on the other hand, the cathode material is lithium-ion batteries. The decisive factor of electrochemical performance, the current anode materials can not fully meet the wide use of cheap electric vehicles and industrial storage requirements.
Cathode materials are the most important raw materials for lithium-ion batteries. Different cathode materials have their own advantages and disadvantages. According to the needs of cheap products, the types of cathode materials selected are different. The functional requirements for lithium-ion battery cathode materials in the consumer electronics field are mainly focused on the energy density and safety of lithium-ion batteries. The functional requirements of power battery cathode materials are high voltage, high energy, high power, and wide temperature range. Lithium iron phosphate, lithium manganate and ternary materials are important raw materials for positive electrode materials for power lithium-ion batteries. In terms of power lithium batteries, lithium titanate is a new development direction.