**6. Conclusions**

This paper proposed a cascade adaptive robust control architecture that overcomes the influence of multi-dimensional system uncertainty on control performance. The higherlevel controller regarded the dynamic model error and parameter disturbance as the system uncertainty and adopted the NFTSM control algorithm with RBFNN estimator to generate the steering wheel angle command. The lower-level controller applied MRAC, considering the uncertainty of stiffness and damping coefficient in AFS to realize the accurate steering torque control. The system stability and finite time convergence are proven by choosing the appropriate Lyapunov function. Two simulation scenarios are carried out to validate the feasibility of the proposed control architecture. The simulation results reveal that the RBFNN-based NFTSM has satisfactory tracking performance under different road friction coefficients and has good robustness against varying tire-cornering stiffness. Meanwhile, it has better control accuracy and a faster convergence rate compared with the conventional sliding mode controller. On the other hand, the model reference adaptive steering torque controller could generate the accurate steering torque that follows the steering wheel angle command with the variation in the steering model parameters or under the circumstance that system performance deteriorates.

**Author Contributions:** M.C. and Y.R.; methodology, M.C. and Y.R.; software, M.C.; validation, Y.R.; formal analysis, Y.R. and M.O.; investigation, M.O.; data curation, Y.R. and M.O.; writing— original draft preparation, M.C.; writing—review and editing, Y.R. and M.O.; supervision, Y.R.; funding acquisition, Y.R. and M.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by Natural Science Foundation of Chongqing (cstc2020jcyjmsxmX0496, cstc2021jcjy-msxmX0532), Science and Technology Research Program of Chongqing Municipal Education Commission (KJQN202103401), and The Program for Innovation Research Groups at Institutions of Higher Education in Chongqing (CXQT21032).

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
