Research On Multi-model Switching Control Of The EPS With Hybrid Power Supply For Commercial Vehicles

At present,the hydraulic power steering system widely used in heavy commercial vehicles has the problems of poor road sense and high energy consumption,which is not conducive to the improvement of vehicle driving safety and fuel economy.The electric power steering system has the advantages of variable power assist with speed,energy saving and environmental protection,but it cannot be applied to heavy commercial vehicles due to the power limitation of the vehicle power supply.Therefore,from the view of solving the power limitation of vehicle power supply,an EPS with hybrid power supply for commercial vehicles is proposed.In order to ensure the control performance of each power mode and the stability during power mode switching,this thesis focuses on the multi-mode switching control strategy of the EPS with hybrid power supply.The main contents of this paper are as follows:(1)According to the technical parameters of the target vehicle,the transmission ratio and the current of steering motor of the electric circulating ball steering system assembly are matched.Considering with the advantages of the hydraulic power assisted characteristic curve of commercial vehicles,and the change characteristics of the steering resistance moment of commercial vehicles,the reverse proportion function type of the power assisted characteristic curve of the steering system is designed.The mathematical model of the electric circulation ball steering system is established,and the state space equation of the system is derived.The two degree of freedom vehicle model is established,and the vehicle handling stability simulation model is built in MATLAB/Simulink.(2)The power characteristics of the vehicle power supply and super capacitor are analyzed,and the super capacitor is matched according to the power requirements of the steering motor and other electrical appliances,the mathematical model of the hybrid power supply is established as well.The mathematical model of the half bridge bi-directional DC-DC converter is established,the topology of the semi-active hybrid power supply system is designed,and the model of the hybrid power system is built based on MATLAB/Simscape.The power allocation strategy of the hybrid power supply system is established,and the rationality of the power allocation strategy is verified by simulation.(3)The hybrid automaton model of the hybrid power supply system is established,which realizes the accurate recognition and fast switching of the power mode of the hybrid power system.According to the power characteristics under different power modes,three local controllers,fuzzy PID controller,auto disturbance rejection controller and sliding mode controller,are designed.The multi-mode switching controller based on fuzzy supervisor is designed to control the local controller to switch when the power mode of hybrid power system is switched,so as to ensure the stability of the multi-mode switching process.(4)The multi-mode switching control strategy of the EPS with hybrid power supply is verified by setting typical driving conditions.The results showed that: hybrid automata model accurately identified and switched the power mode of hybrid power supply system;the local controller in different power modes tracked the target quantity quickly and stably;the fuzzy supervisor also effectively guaranteed the stability of the system in the process of switching.The simulation of steering lightness,medium-high speed steering stability and energy consumption of the steering system is carried out.The results showed that compared with the original vehicle's HPS,the steering power of EPS with hybrid power supply increased by 24.13%,the high-speed steering feel increased by 45.79%,and the total energy consumption dropped by 58.09%.(5)The prototype of EPS with hybrid power supply is developed,the rapid control prototype of multi-mode switching control system is constructed based on dSPACE,and the experimental platform of EPS with hybrid power supply is built.The power assisted characteristic test,input-output test and function test are carried out for the EPS with hybrid power supply.The results showed that the EPS with hybrid power supply conformed to the technical specifications of the industry,and the results of the power assisted characteristic test also verified the effectiveness of the multi-mode switching control system.To sum up,the multi-mode switching control strategy of EPS with hybrid power supply proposed in this thesis provides a powerful reference for the stability control of complex mode,and lays a solid foundation for the promotion and application of EPS in the field of heavy-duty commercial vehicles.The EPS system with hybrid power supply effectively improves the driving safety and fuel economy of commercial vehicles.