Comparative study of two types of control loops aiming at trajectory tracking of a steer-by-wire system with Coulomb friction

Abstract

In an era of automated driving, steer-by-wire system seems to be an indispensable component for an autonomous vehicle. Among the many problems concerned, steering control of the system may be arguably the most indispensable part that lay the foundation for the system and is essentially a position servo control problem. Traditionally, the most commonly used control loop structures of the position servo system can be classified into two categories, both considering the current control loop as an essential part. However, this is not necessarily true in practical applications. In view of this, control systems with two different types of control loops based on proportional–integral–derivative controllers have been designed and compared in this paper for trajectory tracking of the steer-by-wire system with Coulomb friction. The aim is to explore the essential differences between the two types of control loops and study the effect of current loop on performance of the system. When properly designed, it can be seen that the asymptotic stability of the control system can be guaranteed. However, the system with type I control loop has a faster response speed, whereas the system with type II control loop has a smoother response. Theoretical as well as simulation and experimental results have been provided in detail, which can contribute to the understanding of the two types of control loops and can be used as guidance not only for researchers but also for engineering practice.