The Design Of Battery Management System About Lithium Iron Phosphate In Pure Electric Vehicle

In recent years, with the rapid development of automobile industry, the continued growth of traditional car ownership accelerates the consumption of fossil energy and cause serious exhaust pollution. The pure electric vehicle has become the direction of cars because it has the advantages of zero emissions, low energy consumption, low noise and easy maintenance. The Lithium Iron Phosphate has been regarded as the most suitable power source so far for it is high energy density and output power, excellent charge and discharge characteristics. When the lithium iron phosphate is under using, it is necessary to assess the state of batteries, balance the voltage and ensure the safety, so an excellence battery management system has great significance on the entire battery safety and performance.This paper planned the system functions according to actual usage, determined highly integrated system structure, analyzed and designed the key technologies of the system, including through analyzing the properties of lithium iron phosphate and the existing method of estimate SOC, proposing a SOE calculate algorithm which is based on the power integral to replace the SOC value of batteries. In terms of collecting the status of batteries, using the LTC6803-4 to get the precise voltage and temperature of batteries and the open-loop current sensor combining the op-amp circuits & digital filtering to get the electric current value; Designing the CAN bus communication protocol achieve the information exchange with others; Completing the insulation test by establishing the model between the batteries and vehicle. As for the thermal and safety management, the multiple electromagnetic relays are controlled by the result of batteries' status and insulation test; The balance between batteries takes the method of passive balancing strategy; Finally, completing the design of hardware and software about battery management system.Established a rapid charge-discharge platform to debug and test the hardware and software of battery management system, the result shows: the BMS has highly accuracy of voltage, temperature and current; the deviation of SOE value is under 5%; the communication of CAN is stable; the effect of passive balance is obvious; the thermal and safety management is reliable.At last, install the BMS to the vehicle and carry out testing, After near 3000KM's test, it shows the SOE value can reflect the energy status of batteries and can predict the remaining mileage well, and every function works reliably and stably. The BMS reach the expected design effect well.