Study Of Coordinated Control Strategy For PHEV Based On Driving Mode Switching

New energy vehicles which can save energy resources and protect the environment have become the focus of the research and production in auto industry.Due to the technical bottle neck of the battery,and the high cost and the safety performance of the Fuel Cell Vehicle(FCV),the Hybrid Electrical Vehicles(HEV)integrating the traditional internal combustion engine and the electrical motor are still the research emphasis at present.For multi-driving modes co-existing in the HEV,the torque fluctuation,the power interruption and the gear shifting jerk may be produced during the driving mode switching processes,so the match and the optimality of the power sources,the coordinated control to maximize the vehicle efficiency during the dynamic processes are the essential techniques to solve these problems.In order to reduce the output torque fluctuation during the driving mode switching processes,optimize the vehicle efficiency and improve the fuel economy,aiming at a parallel hybrid electrical vehicle(PHEV),this paper mainly implements the following research work:Analysis for the powertrain structure and characteristics of the PHEV: The structural characteristics of the parallel hybrid electric vehicle with planetary gear set are analyzed,the coefficients of the Internal Combustion Engine(ICE),the battery and the motor in the powertrain are illustrated,and their dynamic models are established.By using the vitual lever method,the characteristics of the planetary set are carefully studied.The multi driving modes are illustrated to further the research of the coordinated control for torque fluctuation suppression and vehicle efficiency optimality.Study for the coordinated control strategy during driving mode switching for the PHEV: the target torque requirement is predicted by using the Model Predictive Control method based on Bayes inference.The demarcations of the driving modes are set up based on the oil-electricity transferring efficiency and the powertrain efficiency,and the torque requirement of engine and motor in various operating modes for the hybrid electric vehicle are determined.Based on best efficiency criterion,the torque distribution strategy is designed.According to the different characteristics of the main components,the control methods for the ICE,the motor and the clutch are determined,further on the basis of the clutch state during the driving mode switching processes,all the driving mode switching process are classified into three types.For the switching from motor-only mode to the mode that the ICE need to be started during the motoronly mode,the control strategy of using the motor torque compensating the ICE torque is proposed;for the switching that the clutch need engagement during hybrid driving mode,the coordinated control strategy of motor speed control integrating the clutch pressure control is proposed;for the switching of the total output torque change under the complete engagement state of the clutch,the coordinated control strategy of control the changing rate of the throttle integrating the motor torque adjustment according to the estimation of the ICE out-put torque is proposed.For the confliction between the driving mode switching and the fuel economy,the control of constraining the driving mode switching according to the optimized SOC under the specific driving situation is proposed.This paper presents a new hierarchical optimal control designing to execute the real-time optimization on the basis of a model predictive control concept.The proposed control architecture suggests a hierarchical coordinated control subjected to the related constraints according to the changing rate of different parameters.The prime controller optimizes the best trajectory of the state of charge according to the load detected by a load prediction module,while the second controller will apply the out-put signal from the prime controller along with the signal from the prediction module and the driver inputs to control the powertrain.Additionally,a new methodology to predict the future load imposed on the wheels is detailed introduced.Study for the coordinated control strategy to achieve maximum efficiency for the PHEV powertrain system: a coordinated control strategy is presented to maximize the powertrain efficiency.According to the charging and discharging situation of the battery under different driving mode,the equivalent fuel consumption models are established.On the basis of deep analysis of the efficiency of the internal combustion engine and the battery,a unified expression of the total efficiency is proposed,further a map of the power distribution factor under different power requirement and different state of charge is constructed.According to the total efficiency formula acquired,a coordinated control strategy is then produced with instructions for the optimal power distribution factor between the ICE and the battery,this control strategy can be firstly computed off-line and then can be operated in real-time at a low computation cost.Establishing the Hardware In Loop(HIL)simulation platform and applying other resources to verify the math models,the control models and the control method.The related control strategies are also verified to show the effectiveness in reducing the torque fluctuation,improving the powertrain system efficiency and the fuel economy.The coordinated control strategy aiming at reducing the torque fluctuation is also verified through Matlab/Simulink.The coordinated control strategies of the torque fluctuation suppression and the efficiency maximization are presented and verified in this paper,the simulation results are in good accordance with the experimental results,which means the effectiveness of the proposed coordinated control strategies.The research results provide a theory basis and experiment methods for industrialization of HEV.