| At this stage,electric vehicles have become a hot research topic in the automotive industry,and the state has also vigorously supported the electric vehicle industry in policy.This topic takes this opportunity to design a lithium battery management system for solving the problems of low voltage of lithium battery pack,difficulty in estimating battery power and unbalanced voltage of lithium battery pack in electric vehicle.Battery management system is the key part of electric vehicle and the core of energy system,The system can collect battery voltage,cell voltage,charging and discharging current and battery temperature parameters,and accurately estimate the battery charging status,effectively prevent the battery from under-voltage,over-voltage,over-current,over-temperature,over-charge,over-discharge and other dangerous conditions,to ensure that the battery works in the optimal state.The SOC value methods of battery pack,such as charge accumulation method,open-circuit voltage method,internal resistance method,load voltage method,neural network algorithm and Kalman filter algorithm,are compared and analyzed,and the influencing factors of SOC value estimation are analyzed in this thesis.Finally,the extended Kalman filter algorithm is selected to estimate SOC value.Simulink is used to build the simulation model of lithium iron phosphate battery,and the model is validated.PIC18F46K80-I/PT is chosen as the main control chip in the system hardware design.The front-end acquisition circuit uses BQ76930 to collect battery information.A low power circuit is designed to reduce the functional loss of the system under non-working conditions.The system adopts passive equalization strategy to improve battery efficiency.The system software design uses the extended filter Kalman algorithm to calculate the remaining battery power at k-1 time according to the initial value of the remaining battery power,and uses the estimated error value of the system to constantly modify the current estimated remaining battery power.Programming software is used to write program code,and finally the system is built.Finally,eight lithium iron phosphate batteries are selected to build a test platform,and the battery management system designed in this paper is tested,and the functions of each part of BMS system are tested.The experimental results show that the accuracy of single voltage detection reaches 0.5%,current detection reaches 1%,temperature difference range is controlled at 1℃,and the estimation accuracy of SOC value which meets the industry requirements is less than 5%.The system basically achieves the expected results. |
