Research On Energy Management Strategy Of Electric Vehicle Composite Energy Storage System

With the aggravation of the ecological environment and the shortage of non-renewable fuels such as crude oil,the automobile industry is facing severe challenges.Countries around the world have also accelerated the transformation from traditional energy vehicles to new energy vehicles.Electric energy,as one of the clean energy,is widely used.Meanwhile,electric vehicles have become one of the main development directions of new energy vehicles.However,electric vehicles use "three electrics" to replace the engine and fuel tank of traditional vehicles.The corresponding power devices are greatly increased and the heat loss is also increasing.Increasing the system voltage of the whole vehicle can reduce the system current under the same power.The purpose is to reduce the heat loss of power devices.However,increasing the vehicle system voltage will greatly increase the device cost,and the ultra-high voltage charging technology is not yet mature and difficult to popularize,so the voltage platform above 800 V is only used in a few high-end vehicles.It is an important direction to combine high energy density battery and UC with high power density into a hybrid energy storage system.Based on the background of large heat loss of electric vehicle system,this paper studied how to reduce the heat loss of the system under the premise of meeting the power demand and energy demand of vehicles,so as to improve the energy utilization rate of the whole vehicle.The discussion and innovation include:(1)The whole vehicle system voltage is divided into two voltage platforms,they are 400V(power battery terminal)and 800V(ultra capacitor terminal).And the 800 V platform is connected with the power motor system to reduce the line heat loss and device loss in the system.Different from the existing hybrid energy storage system,the commonly used bidirectional Boost-Buck DC / DC converter is replaced by unidirectional Buck DC / DC converter and control switch.This can reduce device costs and improve energy utilization.In order to reduce the cost of devices and improve the energy efficiency and compared with the existing hybrid energy storage system,the unidirectional Buck DC/DC converter and control switch are used to replace the original bidirectional Boost-Buck DC/DC converter.The configuration adopted in this paper fully combines with the braking energy recovery technology of electric vehicles,which can give full play to the characteristics and advantages of UC,and boost the utilization rate of ultra capacitor,improve the system voltage,and reduce the heat loss of power devices in the system.Further,to establish the topological foundation for the following research work.(2)Based on the charge and discharge tests of power battery and ultra capacitor,the characteristics of energy storage components and other key components are analyzed,and the theoretical basis of parameter matching of new energy storage system are constructed.In view of the new topology,the key parameters of power battery,ultra capacitor and power motor are matched under the background of performance requirements based on cycle conditions,which provide data support for the next step of vehicle model building.(3)Mathematical models of power battery,supercapacitor and DC/DC converter are built based on Simulink.According to the four working modes and the new topology,an adaptive logic gate limit control strategy is proposed.The secondary development of ADVISOR 2002 is carried out to develop the simulation model of pure electric vehicle with composite energy storage system containing logic threshold control strategy.That was based on the US urban cycle conditions(CYC＿UDDS)and the European cycle conditions(CYC＿NEDC).Simulation results show that the composite energy storage system combined with the braking energy recovery technology of pure electric vehicle greatly improves the utilization rate of super capacitor.The improvement of the platform voltage of the ultra capacitor significantly improves the system voltage of the electric vehicle,and meanwhile reduces the current flowing through the power devices.What’s more,it effectively reduces the heat loss of power devices and wiring harness at the load end.The dynamic properties and endurance capacity of the EV was improved.At the same time,the addition of ultra capacitor avoids the impact of high current on the battery,reduces the internal temperature of the power battery when it works,thus reducing the energy loss of the power battery.The power consumption per 100 kilometers of vehicles under UDDS is reduced by 11.6%,and that under NEDC is reduced by 10.1%.