Hierarchical Multi-mode Switching Coordinated Control For ISG Full Hybrid Electric Vehicles

HEVs(Hybrid electric vehicle)have several operration modes,and there exist mode switching processes during driving,the HEV mode swithcing coordinated control for the swiching processes is vital for improving the car fuel economy,reducing exhaust emissions and making its driving comfort better.In this paper,a kind of ISG-FHEV(Full Hybrid Electric Vehicle with an Integrated Starter and Generator)is researched,and its modes are devided into two layers of modes,which include the layer of working modes and the layer of electric-driving modes after analyzing the switching process of its operation modes on the basis of modeling its driving system,and then a hierarchical multi-mode switching coordinated control strategy is put forword.Firstly,the mode switching control strategy between the ISG-FHEV working modes is designed.By analyzing the steady-state efficiency of the engine and the working characteristics of the battery,the switching rules between the ISG-FHEV working modes are made with the torque,speed demanded for the automobile and the SOC(state of charge)of the battery being the hierarchical control basis.On the basis of the rules made above,the ISG-FHEV working modes are devided into singledriving modes,braking modes and hybrid modes,and then a torque distribution strategy based on rules is devised in the first two kinds of modes;In addition,a torque allocation strategy on the basis of the optimal control is designed in the third kind of modes,respectively.Secondly,the mode switching control strategy between ISG-FHEV electric driving modes is worked out.Its working efficiency in each electric driving mode is obttained by analysing the energy-balance process of the electric driving system.According to the efficiency-maximization principle,the switching rules between the electric driving modes are established,so the target mode can be selected,and the target torque of the two motors in the target electric driving mode can be determined at the same time.Then,a dynamic coordinated control strategy is designed.With analyzing the mode switching processes of ISG-FHEV,its driving modes are divided into two kinds of mode switching process,the one is accompanied with starting engine,and the other one without starting engine.Then,the dynamic coordinated control strategies aredesigned for the two kinds of switching processes.Finally,in the joint simulation situation of Matlab / Simulink and Advisor,the control strategies designed are simulated.The simulation results show,with the modeswitching strategy between working modes,the ISG-FHEV engine and battery work in high-efficient area,the car fuel economy is increased obviously,there is a certain degree of reduction in its exhaust emissions,and the optimal performance of the mode switching strategy is close to the global optimal Pontryagin's Minimum Principle strategy;with the mode switching control strategy between electric driving modes,the working efficiency of the ISG-FHEV electric driving system is increased by about7.5% compared with the single-motor electric driving system,achieving the goal that the strategy can switch the electric driving modes high effectively;with the dynamic coordinated control strategy between operation modes,the impact of the vehicle is decreased from 15m/s3 down to 3m/s3,thus improving the driving comfort of the car,effectively.