Electric Power Steering (EPS) facilitates easier steering and has become widely equipped in modern vehicles. Many prior studies on EPS control have tended to overlook the effects of nonlinear friction and parametric uncertainties, while traditional control strategies often suffer from overshooting, phase lag, and chattering. This article proposes a nonlinear robust control scheme that integrates smooth Sliding Mode Control (SMC) with Nonlinear Active Disturbance Rejection Control (NADRC) to address these challenges. The influence of nonlinearities and uncertainties is compensated in the control law through an augmented variable estimated by a Nonlinear Extended State Observer (NESO), and the reference signal is smoothed by a Nonlinear Tracking Differentiator (NTD). Simulation results demon…

4. Conclusion This article presents the design of the robust control approach for the EPS system that explicitly accounts for the effects of nonlinear friction and parametric uncertainties. The proposed controller, developed by integrating smooth SMC and NADRC, aims to reduce tracking errors and minimize energy consumption. Simulation results confirm that the outputs closely follow the reference signals even under nonlinear and uncertain conditions. Furthermore, overshooting, phase delay, and chattering are effectively eliminated when the proposed strategy controls the system. Despite its effectiveness in EPS control, several drawbacks remain. Firstly, the observed error of the augmented variable is relatively large. Secondly, the tracking error of the motor current is significant under adverse conditions. Finally, the control parameters should be tuned adaptively to improve system performance across different operating conditions. These issues are expected to be addressed in future work.

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