Modelling and Position Control of an Electric Power Steering System

This paper presents the modelling, control and analysis of an axle parallel electric power steering system used for autonomous driving. The purpose of the controller is to ensure accurate and robust following of desired trajectories of front steering angle as well as to deliver a smooth steering wheel movement. Firstly the steering model shows how all nonlinearities for the elastic elements, frictions and gear ratio are considered. This model is linearised for the controller design. Thereafter open loop behaviour of the model is examined to determine system resonances. Next a controller synthesis using a Linear Quadratic Integrator controller as well as pole placement is developed. The performance of these controllers is presented in simulation. These results show good tracking performance from the two approaches presented and supports the use of a state space controller design approach in dealing with the various requirement of steering angle control for autonomous driving.