The Design And Implementation Of The Acquisition Boards Of The Battery Management System

With the energy and environmental protection problems increasing prominent, automobile industry of all countries will focus on the research and development of new energy vehicles, which regard battery as the main power. But performance and safety problems of the battery has restricted the commercial of new energy vehicles. Therefore, battery management system which can alleviate these problems has become the focus of research. Battery management system is mainly composed of battery management unit and local control unit AECU. The main function of battery management system is to correctly estimate the charged state of the power battery, dynamically monitoring the working state of the battery pack and battery equalization. This paper deeply studies the difficult point of technology and the existing problems on battery management system at the present stage. Now, the difficult point is the precision of SOC estimation and active equalization problems. High-precision battery data detection is the key to solve these two problems. Therefore, it is necessary to design a high-precision of acquisition boards AECU.According to the requirements of the project, first of all, this paper designed the scheme of realization of the acquisition boards AECU. The function of the acquisition boards AECU include the follow items: dynamically measure the voltage of 24 battery cell, and the measurement error is less than 2.4 mV; measure the temperature of 4 sampling point, and the measurement error is 0.5 ?; Communicate with the battery management unit and active balance board through CAN bus. In addition, the acquisition boards AECU can adjust the voltage through the passive equalization,and accomplish thermal management through controlling fan.Secondly, this paper designed the hardware circuit and device driver of the acquisition boards AECU. The hardware circuit of the acquisition boards AECU consists of a main controller(MC9S12P128) circuit, voltage sampling(LTC6804-2) circuit, temperature collection(DS18B20) circuit, SPI isolation communication circuit, CAN communication(ISO1050)(LM2596) circuit and power supply circuit. Master control chip MC9S12P128 and battery state detection chip LTC6804 communicate through the SPI bus. Master control chip and battery management unit communicate through CAN bus. In the process of device driver design, this paper solved the problem of dismatch of SPI time sequence between MC9S12P128 and LTC6804.Again, this paper designed the software of the acquisition boards AECU. The software has realized the dynamic voltage detection, temperature detection and CAN bus communication. According to the detected voltage value, this paper designed the strategy of balance, to discharge the battery cell which is uneven; According to the detected temperature, this paper designed the strategy of fan control, to accomplish thermal management of the power battery. Then, this paper realized CAN communication protocol of the Intranet of the battery management system. In addition, this paper designed the upper computer of the BMS acquisition boards to display the battery data.Finally, after software and hardware design has finished, collect the acquisition boards AECU with 96 lithium batteries and conduct joint debugging with battery management unit. The debugging results showed that the system is stable and reliable, the average voltage measurement error of the battery is far less than 0.5%;Temperature acquisition error is less than 0.5 ?;CAN communication can be transmitted according to the normal logic, send periodic error of CAN bus is less than 10%. Meet the design requirements.