Optimization Design And Control Of Dual-voltage HEV Compound Power Based On Analysis Of Thermal Characteristics

Nowadays energy shortage and environmental pollution problems have becomeincreasingly prominent, development of energy-saving and new energy vehicles is puton the agenda, but cost and safety issues of high-voltage power supply group hinderthe development of pure electric vehicles. In order to minimize cost to improvevehicle fuel economy and take into account the battery thermal problem influence ontheir performance, this paper improved existing traditional light vehicles for mildhybrid vehicle with dual-voltage compound power in order to improve vehicle energyefficiency and consider the battery thermal problem, analyzed the battery thermalcharacteristics, optimized the structure and control to realize compound power systemintegrated design and control. The main works of this paper are summarized asfollows:Firstly, the effects of temperature on battery performance was analyzed, andstarting from the theoretical analysis of the lithium-ion battery heat generation andheat transfer mechanism, made a preliminary analysis of its temperaturecharacteristics based on a battery charge and discharge test, it proved that compoundpower design based on thermal characteristics is necessary.Then, analyzed the components characteristics of compound power system anddetermined the dual-voltage compound power system configuration and basicparameters, built mild hybrid vehicle with compound power simulation platformusing the forward vehicle simulation software AVL Cruise, and used Matlab/Simulink to build compound power Control strategy, got charge and dischargecurrents versus time of battery pack in the whole cycle through a joint simulation, andsimulated its dynamics and fuel economy and compared with the original car, thesimulation results showed that the control strategy can be formulated well to realizevoltage and current control of compound power system and improved fuel economy. Thirdly, according to the lithium-ion battery heat generation and transfercharacteristics, obtained the relevant thermal parameters, defined the boundaryconditions and established a three-dimensional lithium-ion battery electrochemical-thermal coupling model, and used computational fluid dynamics simulation softwareFluent to simulate battery pack thermal field to provide a theoretical basis for itsthermal structure design. Through analysis of the current battery pack heat transfermedium and cooling structure, this paper adopted air cooling and designed threemajor cooling structures, then made battery pack flow field simulation comparison tofinalize the arrangement of battery cells and cooling structure.Finally, chose a suitable DC/DC converter topology and battery super-capacitorparameters, and control theory of the system components was analyzed. In drivingcycle conditions simulated three-dimensional temperature field of the battery pack,combined with compound power thermal analysis in the vehicle driving cycle todetermine the compound power system layout and control.The proposed design and control of compound power system based on thethermal characteristics can improve their working conditions, extend the life ofcompound power and improve vehicle fuel economy. It is conducive to achieve thegoal of fuel economy to some extent.