Study On Control Of Electric Power Steering System

Electric Power Steering System is a new type automobile power steering system. It has the advantages of simple structure, light weight, small volume, saving fuel, producing less pollutions, and convenient installation and maintenance compared with traditional power steering system. EPS can provide steering assist torque directly by motor. The curve of power-assisted characteristic determines the value of steering assist torque which is analyzed, accounted and controlled by ECU. It can real-time provide reasonable steering assist according to the status of the automobile movements. EPS can meet the requirements of the excellent maneuverability for low speed and the stability for high speed. It has become the focus of study on power steering technology in today.This thesis firstly introduce advantages,study present status at home and abroad,composition-structure,operation principle of the electric power steering system. This thesis analyzes selecting scheme of every component. Based on the brief introduction to the type and selecting scheme, the curve of power-assisted characteristic used in this thesis is determined through calculation.Secondly, on the basis of MC9S12DG128 of Freescale being used as control ship on hardware, power supply circuit,torque signal processing circuit,speed signal processing circuit,driving motor circuit,electromagnetic clutch circuit,Current sensors'signal processing circuit are designed in this thesis. This thesis briefly analyzes structure of motor,operation principle of motor,PID control and found mathematical model of motor.Finally, simulation model of EPS is created by MATLAB/simulink.The method of digital PID current control is applied to the control of motor. The closed loop PID control of target current is finished according to the current forms of assist characteristic. The result of simulation indicates that EPS system has EPS control system has well-behaved power assist ability,tracking performance,stability and can meet the requirements of the excellent maneuverability for low speed and the stability for high speed.