Nonlinear Hybrid Impedance Control for Steering Control of Rack-Mounted Electric Power Steering in Autonomous Vehicles

In this paper, we present an innovative approach to steering control, based on torque overlay, for the smooth and efficient transfer of the steering control from an autonomous driving system to the driver, and to control the pinion angle of the rack-mounted electric power steering for lateral control of an autonomous vehicle. The novelty of our approach lies in the formulation of hybrid impedance control, which employs steering control for both lateral and impedance controls. The proposed method, nonlinear hybrid impedance controller, consists of desired impedance pinion angle generator and a super-twisting sliding mode controller for pinion angle tracking. The desired impedance transfer function of the driver’s torque to the steering wheel angle reflects the driver’s torque to the steering control. The desired impedance pinion angle is generated using the desired impedance transfer function and the desired pinion angle derived by the lateral controller. The sliding mode control method is designed, based on a super-twisting algorithm for the pinion angle, to track the desired impedance pinion angle. Consequently, without the driver’s torque, the proposed method is activated as a pinion angle tracking controller for lateral control of an autonomous vehicle. Moreover, with the driver’s torque, the proposed method is activated as an impedance controller.