Electric motor steer-by-wire angle tracking by proportional differential sliding mode controller with disturbance observer

This paper focuses on the front wheel angle tracking control problem of the steer-by-wire system subject to unmodeled dynamics, uncertain parameters, external disturbances and measurement noises. Considering the measurement uncertainties of front wheel angle and angular velocity, a new steering dynamics model with matched and unmatched disturbances is built for control design. An unmatched disturbance observer is designed to attenuate the effects of unmatched measurement uncertainties and further improve the angle tracking precision of steady-state. A matched disturbance observer is developed to cancel the effects of matched disturbances, and to alleviate the chattering of sliding mode control. Based on the outputs of these two disturbance observers and the sliding mode controller (SMC), a proportional differential sliding mode control (pdSMC) approach is developed by a new sliding manifold for angle tracking of the steer-by-wire system. The developed approach has been downloaded into a steering control unit, and tested in real-world conditions using vehicle test bench to fully realize electric motor steering by wire in engineering practice. Experimental results show that compared with the SMC controller, the pdSMC controller reduces the mean absolute error of the front wheel angle by 52% and 58.9% in the steering tests of step response and slalom path, respectively.