Researches On Optimal Control Strategy Of Dual Planetary Hybrid Electric Vehicle

The hybrid electric vehicle with double planetary row structure can make the vehicle achieve a rich working mode by increasing the clutch and brake,thus improving the power and fuel economy of the vehicle..However,the dual planetary dynamic coupling mechanism also puts forward higher requirements for vehicle control strategy.In this paper,a new type of double planetary hybrid power system is taken as the research object,and aiming at the steady torque distribution problem of different power sources and the torque ripple problem in the mode switching process,optimization designs about the energy management strategy and the dynamic coordinated control strategy are studied to improve vehicle fuel-economy and the quality in the mode switching process.Firstly,the working characteristics of the dual planetary hybrid power system are studied.Based on the theory of lever method,each driving mode of the dual planetary hybrid electric vehicle is analyzed.On this basis,the corresponding steady-state dynamic equations of the system are established under different modes,and the dynamic characteristics of the engine and motor are revealed,which provide the basis for the design of the dynamic coordinated control strategy.Secondly,the model construction of dual planetary hybrid power system is completed.Based on the energy flow characteristics of the dual planetary hybrid vehicle,the modeling principle of the vehicle is determined.The dynamic model of the dual planet hybrid electric vehicle is established by using AVL/Cruise software.In order to verify the effectiveness of the optimal control strategy,a joint simulation platform based on AVL/Cruise and MATLAB/Simulink is built.Thirdly,the optimal design of energy management strategy is studied.Based on the rich working mode of dual planetary hybrid electric vehicle,the mode switching rule and torque distribution method are determined.The energy management optimization strategy based on model predictive control is proposed,setting the fuel economy and batteries charge-discharge balance as the objective functions,adopting dynamic programming algorithm to get the optimal solutions of the optimal control inputs in predictive horizon,and carrying out the simulation analysis.Finally,a dynamic coordinated control strategy based on engine torque estimation is proposed.Based on the dynamic characteristic equations of the system and the high coupling characteristic of the torque between the engine and the motor of the double planet hybrid power system,a real-time estimation method of the engine torque is proposed.The dynamic coordinated control strategy of the system is established with the idea of torque compensation of the motor,which is verified by the joint simulation.The results show that,compared with the rule-based strategy,the energy management strategy using model predictive control algorithm makes the equivalent fuel economy of the dual planetary hybrid vehicle improved by 4.76% in the NEDC cycle and increased by 5.13% in the UDDS cycle.In view of the mode switching impact caused by the inconsistency of the dynamic response of the engine and the motor,the torque dynamic coordinated control strategy proposed in this paper reduces the longitudinal impact by 73.5% when the pure electric mode is switched to the hybrid drive mode,and reduces the longitudinal impact by 80% accordingly when the hybrid drive mode is switched to the pure electric mode.Therefore,the energy management strategy and the dynamic coordinated control strategy proposed in this paper can optimize the torque distribution of different power components in the steady-state and transient processes of the dual planetary hybrid electric vehicle,improve the fuel-economy and ride comfort of the vehicle greatly,enhance the working quality of the hybrid electric vehicle,and provide the technical support for the optimization design of the hybrid electric vehicle.