Design of a robust angle tracking controller for steering-by-wire systems with angular velocity observer and friction compensation

Steering-by-wire (SBW) systems can enhance driving experience and improve autonomous driving performance. A key challenge is ensuring accurate steering angle tracking in both manual and autonomous driving modes while handling inconsistent command update cycles, the absence of an angular velocity sensor, unmodeled dynamics, and nonlinear disturbances. This paper adopts a cascaded control structure comprising an angle loop and an angular velocity loop, focusing on improving steering angle tracking performance by optimizing the angular velocity controller. The angular velocity is estimated based on the Kalman filter (KF), and the steady-state transfer function of the observer model is derived. By combining the angular velocity observer model and the steering system model, an extended nominal model is established. To improve system robustness in the presence of uncertain steering disturbances and limited actuator capabilities, the closed-loop control law is designed using $H_{\infty }$ control theory. To mitigate the impact of nonlinear friction during steering start-up or direction changes, a LuGre dynamic friction model is designed for feedforward compensation. Finally, CarSim/Simulink co-simulation and vehicle tests are conducted. The results demonstrate that the proposed control strategy achieves excellent performance in both manual and autonomous driving modes.