Influence of motor drive parameters on the robust stability of electric power steering systems

This paper investigates the robust stability of an electric power steering system. The stability analysis is carried out by using an eighth order model of the vehicle and steering system dynamics. The general case where the vehicle becomes unstable at high speed and under wet road conditions is examined. In this situation, the characteristic equation of the linearized vehicle model has roots in the right-half complex plane. The vehicle is stabilized by the use of yaw and lateral acceleration state feedback to the electric power steering assist mechanism. It is shown that the vehicle is robustly stabilized for large variations in the vehicle dynamics and motor drive parameters.