Optimization Control Of Smooth Mode Switching In A Hybrid Power System

During the development of new energy automotive industry,Hybrid Electric Vehicles(HEV)are considered as the most practical compromised solution from the traditional internal combustion engine driving vehicles to pure electric vehicles for their structural advantages and relatively mature technology accumulation.In the process of HEV technologies development,the coordination control of multi-modes switching has become one of the most important control problems in hybrid power system.This paper is supported by the National Natural Science Foundation of China Project:The dynamic modeling and optimal control of a dual planetary HEV energy management based on hybrid system theory.Based on a coaxial parallel hybrid vehicle mode switching quality issue,the model predictive control(MPC)algorithm was introduced to plan the output torque of each power unit during the mode switching instant,in order to achieve a smooth mode change.Firstly,a typical mode switching process of HEV is analyzed.Starting from the power coupling system of HEV,the torque output characteristics and transfer characteristics of the engine,the driving motor and the clutch are analyzed.The processes of the engine to join or withdraw from the driving system were emphatically studied and the clutch was determined as an important enabling unit for mode switching.On this basis,the evaluation indexes of the mode switching control effects were established,the switching effects were evaluated from the switching time,switching impact and clutch wear.Secondly,the coordination control problem of HEV during pure electric driving mode to combine driving mode was planned.Based on the vehicle control,a steady state energy control strategy was developed to manage the torque identification,mode selection and torque distribution of the hybrid system.After full understanding the principles and applicability of MPC algorithm,the algorithm was introduced for the transient switching process of pure electric driving to combine driving mode to coordinate the engine,motor and clutch torque.The coordinated controller includes: establishing a clutch-control oriented discrete linear model of mode switching;calculation of states and output values in the prediction domain;formulating and solving the optimization objective function withconstraints;application of the output optimal control signals on the controlled system.Finally,based on prototype of the actual coaxial parallel hybrid system and the desired control target,a joint simulation model was built in the MATLAB/SIMULINK and AVL/CRUISE environment,which was used as the platform to test the vehicle performance and verify the actual effectiveness of the control strategy.Based on the joint simulation platform,a series of simulation experiments were implemented,including the comparison simulation between the designed MPC control strategy and the traditional motor torque compensation strategy,an analysis of the output of MPC controller and the tests on applicability and sensitivity of the algorithm.The simulation results showed that compared with the traditional motor torque compensation strategy,the designed MPC coordinated control strategy could achieve better performance in the model switching impact,the clutch friction work and mode switching time.The simulation designed to test the outputting characteristics of the algorithm showed that the controller can track the reference signals quickly,which showed the effectiveness and real-time performance of the algorithm.The sensitivity tests of the switching threshold and the weight coefficients of the engine and the motor torque provided accurate parameter settings for the stable operation of the system.