I. Introduction
With the increasing attention to intelligent unmanned systems, wheeled mobile robots (WMRs) have attracted significant attention in transportation and intelligent driving due to their versatility and adaptability [1]. However, some research challenges and difficulties still exist in this field. A key issue is the nonholonomic constraint that restricts the system from freely manoeuvring within the entire state space [2]. Besides, how to effectively handle nonlinearities and input constraints simultaneously in a performance-optimizing way is still challenging for trajectory tracking control problems.