Friction compensation control for electric power steering systems

This paper considers friction compensation control problems for electric power steering systems (EPSs) of vehicle. According to the requirement analysis of vehicle assistant control, a mathematical model of EPSs is established, and a double closed-loop control system structure is proposed. Based on the assist characteristic of the desired steering wheel torque, we design a torque control law with mechanical friction compensator and a current control law and with electrical friction compensator respectively. Theory analyses shows the double closed-loop control system structure can make the output torque applied to the steering wheel at different mechanical friction torques are always close to the desired steering wheel torque, and the control laws with friction compensators can make starting steering wheel is smooth. Simulation results show the control system structure and the friction compensation control strategy are easy to implement and the control effect is better.