Research On Energy Management Strategy Of Composite Power Supply Based On Road Slope Information

The advantages of electric vehicles in energy saving and environmental protection are particularly prominent.However,the battery in the current market has the disadvantages of low power density and short cycle life.The driving conditions of the vehicle are complex and changeable,and the electric vehicle with a single battery can not meet the needs of the vehicle.Supercapacitor is a new type of energy storage device,which has high power density,long cycle life,wide working temperature and environmental protection.It is particularly important for the development of electric vehicles to study the composite power system composed of battery and supercapacitor.In order to give full play to the advantages of battery and supercapacitor to achieve the complementary effect and improve the performance of vehicle,the energy distribution strategy of composite power system plays a key role.In this paper,the energy management strategy of composite power system of electric vehicle is studied,the main contents are as follows:(1)Analysis of component characteristics of composite power system.Firstly,the working principle of the battery,the energy storage mechanism of the supercapacitor,the charge and discharge characteristics,the internal resistance characteristics and the energy efficiency of the battery and the supercapacitor are studied and compared,and the boost and depressurization working principle and conversion efficiency of the DCDC converter are studied and analyzed.It lays a theoretical foundation for the parameter matching of composite power system and the simulation of energy management strategy.(2)The structure and parameters of the composite power system match.Based on the analysis of the existing four kinds of composite power system topology,considering the efficiency,stability and cost of the system,the structure of supercapacitor and DCDC series connection is selected,and the battery is connected to DC bus;for the small four-wheel independent drive electric vehicle composite power system,according to the relevant parameters of the vehicle,the power performance is guaranteed,and the battery and supercapacitor charging and discharging constraints and DC-DC are considered The converter converts the power,matches and selects the parameters of the relevant components.(3)Energy allocation strategy of composite power system.Based on the analysis of the shortcomings of the commonly used energy allocation strategies based on vehicle speed and fuzzy control,an energy allocation strategy based on ramp information is designed.Considering the influence of road slope change on the driving demand of the whole vehicle,the vehicle navigation system,including geographic information system and global positioning system,is used to estimate the information of the driving path ramp,and the road slope energy consumption prediction model is designed.Predicting and calculating the energy consumed or needed to be recovered by the supercapacitor in advance,planing the power of power battery and supercapacitor in advance,and controling the SOC of supercapacitor accurately.Making the supercapacitor bear more output power or recover more energy when driving on the ramp,to meet the vehicle's power demand,to effectively reduce the large current charging and discharging of the power battery,to avoid the supercapacitor's over-charging and discharging,and improve the energy utilization rate.(4)Modeling and simulation analysis of composite power system.According to the above theoretical analysis,the battery model,supercapacitor model,vehicle driving dynamics model and energy management system model are established by using MATLAB-Simulink model.The simulation experiments are carried out for NEDC cycle in Europe,NYCC cycle in New York City in the United States and ramp conditions respectively.The simulation results include: the performance comparative analysis of single power supply and composite power supply system under the same working condition;the performance comparative analysis of composite power supply system in different energy management strategies under the same working condition and the performance versus score analysis of composite power supply system in different energy management strategies under the ramp condition.The simulation results show that the composite power supply system can effectively reduce the peak current of battery charge and discharge and improve the power performance compared with the single power supply;the energy distribution strategy based on the ramp information can charge and discharge the supercapacitor in advance before the vehicle enters the ramp,adjust the supercapacitor SOC value,and ensure that the supercapacitor has enough energy to provide high-power uphill energy in the uphill process,Avoid over discharge of super capacitor,effectively reduce the discharge power of battery during the uphill process,and reduce the peak discharge current of battery by 14.9%;in the downhill process,there is enough space for energy recovery to avoid over charge of super capacitor and impact of large peak current of battery during downhill process,effectively extend the service life of battery,increase the energy recovery efficiency by 20.4%,and increase the driving mileage.