Energy Optimization And Coordinated Control Of Dual-planetary Power-split Hydraulic Hybrid Vehicle

With the energy crisis and environmental problems becoming more and more serious,the development of energy-saving and new energy technologies has become an important issue facing humanity.Vehicles are the major source of energy consumption and urban pollution,so the application of energy-saving and new energy technologies is of great significance.Hybrid vehicle is developed on the basis of traditional internal combustion engine vehicles.As a transition product,it has many advantages.It can achieve better energy saving and emission reduction effects,and is a better choice before the chemical battery and fuel cell technology achieve a substantial breakthrough.The hybrid system is the system configuration with the most energy saving potential.The hydraulic hybrid system has many advantages such as higher power density,low cost,long life and good low temperature performance.Therefore,the application of the power-split hydraulic hybrid system to traditional vehicle can achieve better economic and environmental benefits.In this paper,the research on energy optimization control and system coordinated control is proposed for the dual-planetary power-split hydraulic hybrid bus.Firstly,based on AMESim,the dynamic simulation model of the main components and systems of the vehicle including the hydraulic pump/motor detail efficiency model is established.Based on the hierarchical control,the steady-state basic control strategy of the VCU is established in Matlab/Simulink.The related functions of the model and the control strategy are verified by joint simulation.Secondly,based on the power splitting phenomenon of the power-split hydraulic hybrid system,considering the real-time efficiency characteristics of the mechanical and hydraulic transmission system,a threeiterative method was proposed to solve the optimal power splitting state of the mechanicalhydraulic coupling system.This enables energy-optimized control with optimal instantaneous efficiency of the system.Then it was compared with the simulation results of the engine optimal control strategy.Thirdly,the system coordinated control strategy was developed for the characteristics of multiple power sources and multiple clutche/brake in the dual-planetary power-split hybrid system.The demand torque analyzed by the driving operation was processed again by the power source state feedback.By adding a “dynamic transitional torque coordination control functional module” and reprocessing the demand torque analyzed by the driving operation based on the feedback of power source state,rapid change of the total output torque of the system during the driving mode switching was solved.Through the dynamic analysis of the mechanical-hydraulic coupling system,the dynamic relationship between the torque change rate of each power source and the vehicle impact was obtained,and the approximate linear relationship between system output torque and the torque of clutch/brake and pump/motor was also obtained during the rear planetary gear shift.Further,coordinated control of the power source torque change and the state of the actuating member was realized.Finally,the energy optimization control and system coordination control were integrated to obtain the VCU vehicle control strategy.The joint simulation results under its control shown that the fuel economy of the system was improved 3.8% compared to the optimal engine control.The impact of the vehicle was also greatly improved during engine start/stop and multi-mode switching,and rear planetary upshift/downshift.In summary,the energy optimization control strategy and system coordination control strategy developed in this paper have improved and expanded the control method of hydraulic hybrid vehicles,it also laid an important foundation for follow-up research and practical applications,and also contributed to the development of energy-saving and new energy vehicles.