Sliding mode control based on active disturbance rejection control for improving performance of an electric power steering system

Abstract

An electric power steering system is essential in improving safety and driving feel. This article presents a robust control method that enhances system performance by addressing two novel issues. Firstly, an assisted torque map is designed based on nonlinear functions to enhance the comfort of the phase transition and eliminate the negative influence of a sudden increase in the value of assisted torque. Secondly, a control mechanism combines active disturbance rejection control and sliding mode control techniques to reduce steady-state errors and eliminate the influence of sensor noise, overshoot, and chattering. The theoretical stability of the system is evaluated through the Lyapunov stability criterion. Simulations are conducted to validate the performance of the proposed algorithm in two specific cases (v₁ = 20 km/h and v₂ = 60 km/h). According to the article’s findings, the root mean square errors of steering column angle, steering column speed, steering motor angle, and steering motor speed obtained from the proposed controller are 0.073%, 0.422%, 0.070%, and 0.310%, respectively. These values are significantly lower than the errors of traditional controllers. Moreover, the ESO’s estimation of all state variables of the system is highly accurate, with no more than 0.6% errors (for the first case) and 1.5% (for the second case). The augmented variable’s observation of external disturbances is also accurate, with a potential accuracy of up to 90%. This high level of accuracy in estimating state variables is a key factor in maintaining system stability under different operating conditions and ensuring that the assisted torque generated by the electric motor closely tracks ideal values, thereby enhancing steering performance and driving safety.