Abstract: The electric motor steer-by-wire system without the road wheel angle sensor faces two major challenges: one is the real-time accurate acquisition of the steering resistance torque; the other is the real-time accurate angle control. This paper designs a low-calculation and high-precision proportional integral observer to achieve the accurate estimation of the system torque. For the steering dynamics presenting the typical second-order series system characteristics, this paper designs a backstepping angle tracking control algorithm. The Lyapunov function is further established to demonstrate that the sensorless steer-by-wire system using the designed control algorithm is asymptotically stable. A real vehicle chassis test platform using the sensorless steer-by-wire system is constructed, and the sinusoidal and slope tests are selected for the validation of the control algorithm. The experimental results show that the proportional integral observer can effectively estimate the system resisting moment, and the backstepping control algorithm based on the the proportional integral observer is able to track the target angle accurately in real-time.

Key words: sensorless steer-by-wire, proportional integral observer, resistance moment estimation, backstepping control, Lyapunov stability