Research On Matching Design And Energy Management Of EPS With Hybrid Power Supply

With the increasingly prominent problems of road traffic safety and vehicle emission pollution,the relevant departments of the state have issued regulations on the technical performance requirements of road transport vehicles,and policies on vehicle fuel consumption limits,etc.,which are guiding domestic commercial vehicles being more safe,reliable and energy-saving.At present,the traditional Hydraulic Power Steering system(HPS)is still widely used in commercial vehicles,which is unable to take both portability of low-speed steering and the stability of high-speed steering into account and further influence the high-speed driving safety.In,addition,HPS causes a large of reactive power loss.In recent years,Electric Power Steering system(EPS)has been widely used in passenger cars for take advantage of excellent safety,energy saving and environmental protection.However,the heavy load on the front axle of the heavy commercial vehicle cause a great demand of steering power which outweighs the discharge capacity of vehicle power supply,which impedes the application of EPS in heavy commercial vehicles is hard.Aiming at the problem that the vehicle power supply restricts the application of EPS in heavy-duty commercial vehicles,an EPS based on hybrid power supply(HP-EPS)system is proposed.In order to ensure the power distribution efficiency of hybrid power supply,this paper focuses on the matching design and energy management strategy of HP-EPS.The main contents of this paper are as follows:(1)The system structure and working principle of HP-EPS are introduced,the rated current parameters of EPS assist motor is calculated and the assist characteristic curve is designed;the EPS demand current is calculated according to the torque and speed signals collected in the real vehicle test under the comprehensive working condition,and statistically analyzes the distribution law of the load current of EPS and other vehicle electrical appliances under the comprehensive working condition.On the basis,the capacitance of the super capacitor and the parameters of DC/DC converter are calculated,and the system configuration of the hybrid power supply is determined by comparison.(2)The EPS dynamic characteristics are analyzed;the EPS mathematical model is established including the mechanical part and the electric power part.Comparing various model structures of super capacitors and considering the model accuracy and complexity,the classic RC model of super capacitor is established.Based on the working principle of the bi-directional Buck/Boost converter,the mathematical model and control model of Buck/Boost converter are built.(3)According to the current components of HP-EPS,an energy management strategy based on optimized rules is designed for the hybrid power system.In order to reduce the fluctuation of the vehicle power supply output current,the difference sum of the output current of vehicle power supply is taken as the objective function,and particle swarm optimization algorithm(PSO)is used to optimize the parameters of energy management strategy.The simulation results show that the proposed energy management strategy based on optimized rules can effectively depress the fluctuation and reduce 33% of output current of the vehicle power supply.(4)The super capacitor model,DC/DC converter model and energy management control model are simulated and analyzed respectively to verify the model reliability of the and parameter accuracy.the HP-EPS is simulated under the comprehensive test condition.The simulation results show that the working efficiency of the vehicle power supply increases by 12.41% which verifies the power distribution of energy management.The auxiliary role of super capacitor in hybrid power supply and the effectiveness of energy management strategy are verified by the HP-EPS bench test.To sum up,the proposed matching design method and energy management strategy of HPEPS system realizes the power distribution of the hybrid power supply,and significantly optimizes the output current of vehicle power supply,which provides theoretical and technical basis for the application of EPS in heavy commercial vehicles and further improves the driving safety and fuel economy of heavy commercial vehicles.