**7. Conclusions**

In this paper, a DDAS control strategy based on the steering-wheel-torque direct control is developed for the first time. Considering the disadvantages of the traditional PID controller and the particularities of the DDAS system, the ADRC technology is introduced to design the DDAS controller to reduce the steering effort of the driver and improve the driver's road feeling simultaneously. As for the problem that the parameters of the ADRC controller are difficult to set, the simulated annealing algorithm is used to optimize the controller parameters offline. Finally, a variety of working conditions are selected to verify the developed strategy by using the vehicle model established in this paper. All the simulation and experiment results show that compared with the PID controller commonly used in DDAS, the proposed ADRC controller developed in this paper can not only reduce the steering effort of the driver obviously like previous conventional control method, but also have better control performance in tracking accuracy and smooth road feeling of the driver.

**Author Contributions:** J.W. administrated the whole research and revised the manuscript as the scientific project leader. X.W. implemented the experiments and wrote the initial manuscript. Z.L. designed the control algorithm model and performed the simulation. F.A. supervised the writing and critically reviewed. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China under Grant 51875235, and in part by the Jilin Province Science and Technology Development Project under Grant 20180414011GH and 20190802015ZG.

**Acknowledgments:** The authors are grateful to the National Natural Science Foundation of China and all the reviewers for their constructive comments.

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