Torque-Overlay-Based Robust Steering Wheel Angle Control of Electrical Power Steering for a Lane-Keeping System of Automated Vehicles

We propose a torque-overlay-based robust steering wheel angle (SWA) control method of electrical power steering (EPS) for a lane-keeping system of automated vehicles. The proposed method consists of an augmented observer and a nonlinear damping controller to guarantee the semiglobal uniform ultimate boundedness of the SWA tracking error using only SWA feedback. The key idea of the proposed method is that the system functions with unknown parameters and external disturbance, along with their derivatives, are combined into an augmented state variable for designing the nonlinear observer in the absence of Lipschitz conditions. The augmented observer is designed to estimate the full state and disturbance. The nonlinear damping controller is developed via backstepping to suppress the angle tracking error using the input-to-state stability property when the estimation error becomes large. Since the proposed method is designed based on torque overlay, a torque integration using basic functions of the EPS for SWA control is available for driver convenience. Furthermore, no modification of the EPS is required. The performance of the proposed method was validated through experimentation with a test vehicle.