Research On Control Strategy Of Engine And Traction Motor During Mode Transition For A Series-Parallel Hybrid Electric Vehicle

With the increasingly serious energy and environmental issues,the vehicle as one of the most important means of transport in people's daily lives,is required to be more efficient and cleaner.Hybrid electric vehicle(HEV)is an effective and reliable solution.Series-parallel HEVs possess the major features of both series and parallel HEVs,and have a strong ability to improve vehicle economy.In order to make energy management optimized,the vehicle should make transition between various modes during operation.However,during mode transitions,especially the transition from pure electric drive mode to engine/hybrid drive mode,involving fast engine start-up,clutch engagement and other transient processes which can affect emissions and vehicle driveability.Therefore,the research of control strategy of engine and traction motor for resolving emissions and driveability problems during mode transition is important for hybrid electric vehicles.At the same time,due to the short duration of the mode transition process,and the highly dynamic changes of the engine,ISG,clutch and traction motor during the transition period,the study is challenging.(1)Based on the rapid prototyping controller development platform Mototron,the basic framework of the engine management system was set up.Using graphical control strategy development software matlab/simulink,the specific engine control function modules are developed,including electronic throttle control,intake air control,fuel injection control,and ignition control.(2)For the problem of emissions and vehicle driveability during mode transition,the engine control strategy during mode transition was researched.Firstly,based on the results of bench tests,the characteristics of traditional engine start were analyzed.When the traditional engine start,the indicated engine torque must be sufficient to realize a successful start.Thus,the intake air control,fuel injection control and ignition control for traditional engine start must consider the requirement of torque output.Meanwhile,the first fire of traditional engine start occurs at a relatively low engine speed,which causes poor combustion conditions.Secondly,analyze the characteristics of the engine start control for a series-parallel HEV,that is,ISG provides auxiliary torque during engine start,engine control strategy can get rid of the requirement of indicated torque output,and control of engine speed and intake manifold pressure can be accurate.Thirdly,the engine control strategy during mode transition is proposed.In detail,the optimization of clutch state was conducted;and the engine operation condition(speed and torque)was optimized to reduce emissions and improve driveability,including the first cycle of engine speed and load,as well as the speed and load trajectory;and the fuel injection quantity optimization,including the fuel injection quantity optimization based on the well-controlled speed and intake manifold pressure,and the fuel injection quantity optimization based on the ignition with high energy.(3)For the problem of vehicle driveability during mode transition,the traction motor control strategy during mode transition was researched.Firstly,the powertrain model for control strategy design and simulation was constructed.Then,the control strategy of traction motor torque during mode transition is proposed.In detail,a part of the traction motor torque is used to meet the vehicle driving requirement,and the other part is used to compensate the clutch torque;and the torque compensation control is composed of the feed forward control based on torque estimation and the feedback control based on reference wheel speed tracking for eliminating the torque estimation error;and the feedback control was designed using the mu-synthesis method based on the system model with parameter uncertainties.The system model is simplified by eliminating the wheel load torque in the control design.Finally,the validity of the control strategy is preliminary verified by pure software simulation.(4)In order to verify the validity of the control strategy further,a hardware-in-the-loop(HIL)simulation is conducted in the paper.Firstly,the HIL simulation platform was constructed,which is composed of the input dynamometer which is used to simulate the engine torque,the real transmission with clutch and the virtual vehicle model which includes the motor,the final drive,the differential,the half shafts,the tires,the vehicle body and road.In detail,the transmission output torque is the input of the virtual vehicle model;and the outputs of the virtual model are the left wheel speed,right wheel speed and input motor torque,which will be transmitted to dynamometer control system for tracking by the left,right and input dynamometers,respectively.The HIL simulation results demonstrated that torque disturbances during mode transitions can be well compensated for with the designed control strategy,and vehicle jerk can be greatly reduced.In addition,the HIL simulation results indicated that the proposed control is adaptable for mode transitions during different driving conditions and robust to parameter uncertainties.