Fixed-time adaptive fault-tolerant control with guaranteed-performance using differential steering for 4WID vehicle considering steering actuator failure

This paper proposes a fixed-time adaptive fault-tolerant control strategy for four-wheel independently driven electric vehicles (4WID-EVs) to address steering actuator failures. The proposed approach ensures robust trajectory tracking and smooth transients during mode transitions by exploiting differential steering. First, dynamic models of the steer-by-wire (SBW) system and differential steering system (DSS) are established, which serve as the foundation for a unified switching system model. An ideal steering angle correction method is derived to preserve consistent vehicle dynamics before and after steering failure. To maintain tracking accuracy despite actuator faults and external disturbances, a predictive-bandwidth extended state observer (PB-ESO) is designed to accurately estimate system states and total disturbances, thereby suppressing transient oscillations during mode switching. Adaptive laws are formulated to address parametric uncertainties and guarantee overall system stability. Furthermore, a fixed-time prescribed performance adaptive backstepping controller (FTPABC) is developed to enable rapid convergence within predefined performance envelopes. A dynamic switching mechanism, incorporating a performance monitoring function, is introduced to facilitate seamless and timely transitions between the SBW and DSS modes. Finally, the efficacy of the proposed strategy is validated through comprehensive simulations and hardware-in-the-loop experiments. The results confirm that the control framework effectively sustains vehicle stability and steering capabilities under actuator failure scenarios.