Research And Design Of Power Battery Pack For Pure Electric Vehicles

This subject does the research of power battery pack for pure electric vehicles, chooses the NCR18650PF lithium-ion battery as the basic cell, and designs the multi-layer battery system architecture from battery cell and battery unit to battery pack. Based on designed architecture, this subject does characteristics experiment for the battery cell, designs mechanical structure for battery unit and battery pack, analyses the heat generation model of battery cell and battery unit, and designs the battery unit state monitoring and protection module.The main works done in this paper are as follows:(1) Lithium-ion battery cell characteristics research:In this part, this subject does some experiments to research characteristics of the battery cell, including constant current-constant voltage charging characteristic, constant current discharging characteristic, the relationship between discharge capacity and open circuit voltage, and the internal resistance of battery cell at room temperature. The results and method of the experiments will guide the characteristics research of battery unit and battery pack.(2) Design of power battery mechanical structure:According to the parameters of electric vehicle's motor, this subject designs battery pack architecture,18 battery cells compose one battery unit in parallel, and 24 battery units compose the battery pack in series. The mechanical structure design of battery pack has fully considered the internal connection, fixation, insulation between battery units, and adopts air cooling mode to decrease the working temperature of internal battery units. The specific energy of the final designed battery pack is 105.68 W·h/Kg.(3) Thermal analysis of battery cell and battery unit:This part builds three dimensional model of NCR18650PF lithium-ion battery cell, including multi-layer structure and the lumped structure. Based on the lumped three dimensional model, this subject does heat generation model simulation under constant current, and the working temperature increment results of battery cell surface under simulation are consistent with the experimental results. This subject also does the thermal simulation for the simplified battery unit under 0.5C and 1C rate constant current discharging situation.Under normal air convection, the temperature increment of two discharging rate are 9.27? and 20.45?. While under the forced air cooling situation, the highest temperature of 1C rate constant current discharging declines 4?.(4) Design of battery unit state monitoring and protection module.In this part, this subject provides hardware design solution of battery management system and divides the hardware into battery unit state monitoring and protection module and main control module. This subject focus on the battery unit monitoring and protection module design, combines the main monitoring circuit and secondary monitoring circuit hardware architecture. The main monitoring circuit realizes the battery unit state data input and balancing signal output, and the secondary monitoring circuit mainly realizes the diagnosis of the abnormal state and transmits the alert signal to main control module.