Research On Modeling And Control Algorithms Of Electric Power Steering System

Miniaturization,lightweight,and energy saving have become the trend of today’s automotive development with the development of automotive electronics technology,.The electric power steering system(EPS)with its main advantages of improving driving comfort,safety and environmental protection is gradually becoming the mainstream of automotive steering technology.Based on research results at home and abroad,this paper focuses on the stability of the basic assist control and the return-to-center characteristic of the return control.The main tasks are as follow:(1)The control strategy,including basic assist control and return control,is designed for improving steering portability and returning performance.The segmented curve-type power assist characteristic curve is realized.The compensator is a second-order filter with three poles to improve the stability of EPS.The effectiveness of the basic power control is verified by the EPS bench experiment.The result show that the compensator module did play a role in improving system stability.(2)In order to analyze the influence of the compensator module,the mathematical model of the column type EPS is established,and the open-loop transfer function of the EPS is obtained.Then,based on the open-loop transfer function,the stability of the EPS is analyzed by classical control theory.And the mathematical model is verified by the frequency characteristic experiment.Combined with the concept of stability margin,the linear stability condition of the EPS system is proposed.(3)In order to maximize the influence of the compensator module,linear system analysis is done.Based on the system model,nonlinear system analysis is carried out by considering nonlinear factors such as assist dead zone,boost gain variation and current limit,then the nonlinear stability condition is proposed.The optimal compensator parameter acquisition algorithm is proposed for the compensator.And the correctness of the algorithm is verified by EPS simulation and bench experiment.(4)The vehicle steering simulation and real vehicle experiment are respectively used for verifying the performance of the designed control strategy.It is found that there is a certain defect in the return control based on the steering wheel angle,and then a return control based on the wheel back torque is proposed.