18650 lithium-ion battery

　　CAN bus 18650 lithium-ion battery management solution

　　Accurate measurement of remaining battery capacity has always been a very critical issue in the development of electric vehicles. An effective battery management system helps improve battery life. Therefore, accurate estimation of battery SOC has become a central issue in electric vehicle battery energy management systems. If the SOC of the battery can be correctly estimated, the power provided by the battery can be rationally utilized and the service life of the battery pack can be extended.

　　The solution adopts bus-type networking and uses fieldbus to complete data exchange between various nodes. In the distributed solution, the multi-energy controller is the main control ECU, which communicates with multiple lower-level ECUs through the fieldbus. During the working process, the communication sub-module of each controller runs in the background in the form of a timer or interrupt to complete the sending and receiving of data and save the main process resource expenditure.

　　The SOC value of the battery is sent by the battery controller to the multi-energy controller through the CAN bus, and the working mode of the vehicle is determined by the multi-energy controller through certain logical algorithms by collecting information from each ECU. Once these parameters are determined, we can decide whether to start the engine or shut down the engine, and also decide in which state the motor should work. For example, when the SOC value of the battery is between 50% and 70%, the multi-energy controller calculates that the vehicle working mode is in the starting mode, which means that the current system has sufficient power energy and there is no need to turn on the engine. Moreover, the motor Can work as a driver.

　　2 System hardware composition

　　The battery controller can communicate with other control systems in the external car through the CAN bus network. A battery management ECU (electronic control unit) and 4 battery pack information detection ECUs; the single cells we use are combined into 24 battery packs. We configure a measurement unit for every 6 battery packs, that is, there are total battery packs ECU1 to ECU4. The 4 battery pack ECUs and the battery pack ECU form a CAN bus network, and a CAN controller and the battery pack ECU form the CAN inside the battery management system. network, another CAN controller and other control systems in the car form a vehicle optical fiber CAN bus network.

　　As shown in Figure 3, the embedded microcontroller used in the battery pack ECU is the p87C591 microcontroller, whose internal hardware integrates a CAN controller and an A/D analog-to-digital conversion module. Each battery pack ECU manages 6 battery packs, and its completed function is to measure the voltage and temperature information of the 6 battery packs, and send the collected information to the battery management ECU through the CAN bus. The voltages of the 6-channel battery pack are connected to the 6-channel A/D input port of p87C591 through the voltage conditioning circuit. The signal lines of the 6 temperature sensors are connected to the same IO port of p87C591.

　　Circuit design of 3CAN interface

　　In this design, p87C591 is used as the microcontroller. Among them, the interface circuit design between p87C591 and CAN driver chip is shown in Figure 4. It is mainly composed of three parts: p87C591, photoelectric isolation circuit, and CAN driver. Photoelectric isolation circuit: In order to further suppress interference, photoelectric isolation circuits are often used in CAN bus interfaces. The photoelectric isolator is generally located between the CAN controller and the transceiver.

　　The overall system program includes the initialization program and the main loop program, and its flow chart is shown in Figure 5:

　　The system is powered on first, and then initializes CAN and timers. The system waits for interrupts. If there is an interrupt, it determines the interrupt type. If it is an interrupt from the SJA1000 controller, it reads the data of the SJA1000 controller and releases the buffer. The operation is completed. Interrupt return, if it is a timer 50ms periodic interrupt, AD conversion is performed on the voltage and current data, the SOC value is calculated, and the relevant data is sent by CAN, and the interrupt returns after the operation is completed.

　　4 Conclusion

　　Data communication technology based on CAN bus has high reliability, real-time performance and flexibility. CAN bus has broad application prospects and development space in the application of nickel-metal hydride battery management systems for hybrid electric vehicles.

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