Study On Energy Management Strategy For CVT Full Hybrid Electric Vehicle Based On Instantaneous Optimization

In the background of energy crisis and environment pollution, the new energyvehicle which has advantages of low energy consumption and low emissions, is apromising domain of future automobile. Because large capacity battery is too difficult togain revolutionary headway in the near future, the development of electric vehicle islimited. So hybrid electric vehicle (HEV) becomes the focus of attention of the wholeworld in a long time.Continuously variable transmission (CVT) is the ideal transmission because it canchange ratios continuously and suit the engine and motor to achieve high performanceareas depending on the velocity and load changes in any driving conditions. So thevehicle equipped with CVT becomes more and more popular.Energy management strategy of HEV includes two aspects: one is to determine theswitching conditions of system operation modes; and the other is to determine thepower-train components matching relationship in operation mode. So energymanagement control strategy is an important factor affecting fuel economy.In this paper, energy management strategy for full HEV equipped with CVT hasbeen taken as the research object. The main researches show as follow:①Based on the Bench-test experiment on power-train components, andcombination the theory of modeling with experimental modeling, the fuel consumptionmodel of engine and efficiency models of engine, integrated starter generator (ISG)motor, battery and CVT are built.②In order to calculate system efficiency of pure electric mode and electric assistmode, the transformation relationship of electricity and fuel should be determined.According to the power sources in the battery, the result of fuel-electric conversionfactor is calculated by obtained energy from charging mode and regenerative brakingmode respectively.③In consideration of battery life and performance, two different driving schemaswhich are plan of energy consumption and energy growth, were proposed. Based oncomprehensive consideration of efficiency of engine, ISG motor, battery and CVT,system efficiency optimization models for driving schemas are developed. According tothe target of instantaneous optimization of system efficiency, operating ranges of eachmode of powertrain are determined and the corresponding energy management strategies are established.④Based on HEV braking dynamics analysis, combined with requirements of theECE regulation, make the control strategy of force distribution between the driveaxies. According to the analysis of HEV regenerative braking mode, establish theoptimization model that is to maximize the battery recovery energy, and gain the targetcontrol torque and ratio of CVT. Then comprehensive consideration of battery SOC andbraking intensity, the control strategy under braking condition is established.⑤Backward simulation model of full HEV with CVT is built based onMatlab/simulink, and then the strategy proposed in this paper has been applied to themodel to simulate under the new European driving cycle (NEDC). Compared with thetraditional vehicle, the simulation results demonstrate that HEV using the strategyproposed in the paper can substantially improve the vehicle fuel economy, and can keepbattery state of charge (SOC) change in a reasonable variation range.