The Research And Optimization On The Energy Management System Of Hybrid Electric Vehicle With Continuously Variable Transmission

In recent years,with the increasing environmental pollution and the shortage of oil resources,the pace of vehicle "electrification" is accelerating.Under the background that electric vehicles can not achieve large-scale commercial application in a short period of time,hybrid electric vehicles are considered to be one of the feasible schemes to achieve energy conservation and emission reduction by virtue of their own advantages of combining conventional vehicles and electric vehicles.Using continuously variable transmission(CVT)in the hybrid electric vehicle can control the speed ratio to change continuously with different working conditions,so that the power source can work in the most efficient area,which provides the possibility for further improving the fuel economy and overall performance of the hybrid electric vehicle.The energy management strategy(EMS)is one of the difficulties of hybrid vehicles.At present,the rule-based energy management strategy has been applied in engineering practice for a long time.However,there are still many bottlenecks in the design and application of optimal control methods.For this reason,based on the National 863 program,a CVT based Hybrid electric vehicle is designed in this paper,and the research of the energy management strategy is conducted in-depth,the main tasks are as follows:(1)Vehicle modeling and model verification.Through the combination of experimental modeling and theoretical modeling,the forward simulation model including driver,power transmission system,vehicle dynamics and vehicle controller is established.The open-loop simulation results and the experimental data are compared and analyzed to verify the correctness of the simulation model,which provides an important basis for the development of control strategy and the research of optimal control method.(2)Hardware and software system development of vehicle controller,and the control signals calculation based on system efficiency optimization.Combined with the characteristics of CVT Hybrid vehicle operation and the functional requirements of the control system,according to the ISO26262 functional safety standard,the hardware and software system of the vehicle controller are developed.The rule based energy management strategy is designed,and the efficiency optimization model of the hybrid system under each working mode is established.By off-line optimization method,the optimal control signals of the system under different working modes is calculated with the highest comprehensive efficiency of the system.(3)Considering the fuel economy and driving performance of the hybrid vehicle,a global optimization method of CVT Hybrid vehicle is proposed based on the dynamic programming algorithm.The backward-facing model of the vehicle is established.The battery SOC is chosen to be the state variable,the torque distribution factor of the power sources and the target speed ratio of the CVT are taken as the control variables,and the dynamic programming algorithm is used to optimize the fuel economy.The dynamic model of CVT hybrid transmission system is established,the driving problem caused by single objective function is analyzed,and an optimization algorithm which can take both fuel economy and driving performance into account is proposed.The simulation results verify the effectiveness of the algorithm.(4)A real-time optimal control strategy is designed based on the adaptive equivalent consumption minimization strategy.On the basis of driving performance optimization,this paper analyzes the trade-off between fuel economy and driving performance in the real-time optimization strategy.In order to further improve the fuel economy and the robustness of the A-ECMS strategy,a driving pattern recognition algorithm based on learning vector quantization neural network model is designed,and the influence of different initial SOC on the optimal equivalent factor is analyzed.On this basis,an equivalent factor adaptive algorithm considering driving mode and battery SOC is proposed.Finally,the effectiveness of the strategy is tested by using the random combination driving cycles,and compared with several kinds of control strategies based on ECMS.The results verify the superiority of the algorithm.(5)Experimental tests are designed to verify the effectiveness of the control functions of the system.In the bench test,the target speed ratio tracking ability of the hybrid CVT assembly is tested,which verifies the feasibility of the overall scheme of the hybrid CVT assembly.The hub test and road test are carried out on the prototype vehicle.The responses of the power source and fuel economy of the vehicle are analyzed.The experimental results verify the effectiveness of the control strategy proposed in this paper.