| Today,with the rapid development of economy,cars have become the main means of transportation for people to travel,and traditional energy cars rely mainly on oil resources.After a long period of consumption,energy is increasingly exhausted,the increase of vehicle use and the increase of exhaust emissions,resulting in a large amount of air pollution.Therefore,the development of new energy vehicles,which is the core of electric vehicles,has been put on the agenda.Electric vehicles are mainly powered by power batteries,and the limitations of battery development have resulted in the inability of electric vehicles to be widely used.When a single power battery is used as the driving energy for an electric vehicle,the impact of a long instantaneous large current can shorten the battery life when the vehicle is climbing or accelerating.Super capacitor is a new type of energy storage element with high power density,which can charge and discharge high power to make up the deficiency of the battery.The composite energy storage system composed of super capacitor and battery is of great significance for promoting the development of electric vehicle industry.This dissertation summarized the current research status of the pure electric vehicle composite energy storage system at home and abroad.Lithium battery and super capacitor and bi-directional DC/DC converter are selected to form composite energy storage system.The type of the battery is analyzed,and it carried out the temperature characteristic experiment and the discharge characteristic experiment.The characteristics of super capacitor are introduced,and it carried out the charge discharge experiment and the self discharge experiment.The structure of bi-directional DC/DC converter is selected,and the bidirectional half bridge DC/DC transformation structure is finally established,and its working principle is analyzed.Finally,the structure of the composite energy storage system is established,making full use of the characteristics of battery with high energy density and super capacitor with high power density to meet the needs of electric vehicles in driving.According to the characteristics of the composite energy storage system,it designed the energy control strategy based on the logic threshold and the energy control based on the fuzzy control.The whole vehicle model is built based on AVL CRUISE software,and the method of joint simulation of CRUISE and MATLAB is analyzed,and it carried out the joint simulation with MATLAB on the road condition of NEDC.Simulation results show that the proposed control strategy can effectively allocate the power of super capacitor and battery,reduce the impact of high current on battery and improve the mileage.Due to the subjectivity of fuzzy control strategy,particle swarm optimization is applied to optimize the control rules of fuzzy control,and the braking energy recovery rate and energy consumption rate are taken as the optimization objectives.The algorithm is compiled in MATLAB,and the Simulink model is rebuilt to optimize the calculation.The optimization results show that the optimized fuzzy controller can improve the energy recovery rate,reduce energy consumption and improve economic performance.The hardware and software design of the composite energy storage system is carried out.The hardware includes the design of current sampling,the design of voltage sampling,the design of CAN communication circuit,the design of auxiliary power supply circuit,etc.The main control chip adopts the DSP TMS320F2812 of TI company.The software part includes the main program design,the AD collection subroutine,the energy management subroutine and the CAN communication subroutine.The experimental platform of composite energy storage system is built,and the energy control strategy of the composite energy storage system is experimentally verified.The experimental results are the same as the simulation trend.The experiment proves the rationality and effectiveness of the control strategy. |
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