Mode Switching Coordinated Control For PHEV Based On Model Predictive Control

Hybrid electric vehicle contains two power sources,which can switch between multiple modes according to driving conditions or driving environment.Due to the dynamic characteristics of the two power sources of engine and motor are different,and there is dynamic changes of clutch engagement or separation during the mode switching process,the phenomenon of power transmission interruption and torque fluctuation are prone to happen,which will cause vehicle chatter and clutch frictional losses,affecting ride comfort and clutch life.Therefore,mode switching dynamic coordinated control for parallel hybrid electric vehicle(PHEV)is studied.Firstly,analyze vehicle structure and build dynamic model.The vehicle inertias are integrated to be two parts: the engine side and the motor side based on analyzing the PHEV system structure.The vehicle longitudinal dynamic model and simulation model are built.Secondly,divide working modes and design rules of the mode switching.According to the states of two power sources and clutch,working modes are divided in the vehicle.According to state of vehicle and whether the states of clutch change or not during mode switching,the switching between the different working modes are divided into different categories.According to the state of charge of battery,the demand torque and the demand speed of the vehicle,the switching rules of each working mode are designed,guaranteeing engine and battery working in the efficient area.Thirdly,formulate mode switching coordinated control strategy for PHEV based on model predictive control and simulation.Firstly,a predictive model is established based on the dynamic analysis of the mode switching process.Secondly,the objective function is constructed based on that the speed response of motor is used as the target speed.Relaxation factor is introduced considering the nonfeasible solution problem of the objective function,and restrictions are designed considering the physical constraints of power components and the limit of the maximum jeck,guaranteeing feasibility of the solution of objective function and the smoothness of the switching,achieving smaller jeck and clutch frictional losses.Finally,the proposed control strategy is simulated and verified.The simulation results show that compared with the traditional control strategy,the jerk and clutch frictional losses of the proposed control strategy obviously decreased during mode switching,guaranteeing the smoothness of the switching and improving the driving performance.Finally,formulate model switching coordination control strategy for PHEV based on cascade predictive control and simulation.In this strategy,the model predictive control algorithm is designed by introducing new control variables,and designing constraints and the objective function of including the clutch frictional losses to obtain the optimal demand torque of the motor,engine and clutch,so that the vehicle jeck can meet the requirements and the clutch frictional losses is minimum.The PID controller of high sampling frequency is applied to compensate engine output torque of each model prediction period and achieve a smooth mode switching.The simulation results show that compared with the model predictive control strategy,the prediction error is obviously decreased and the jerk and clutch frictional losses are further decreased,which verifies the effectiveness of the proposed control strategy.