Integral sliding mode yaw control for in-wheel-motor driven and differentially steered electric vehicles with mismatched disturbances

Differential drive assistance steering (DDAS) is an emerging assisted steering mechanism in in-wheel-motor driven (IWMD) electric vehicles, yielded by the differential moment of the front tires in the steering system. DDAS can steer the front wheels when there is no steering power from the driver or the steering motor, and thus can be used as a redundant steering actuator. To realize the yaw control when the active front steering (AFS) entirely breaks down and guarantee the transient control performance therein, this paper proposes an integral sliding mode control (ISMC) approach for IWMD electric vehicles steered by DDAS. Two contributions are made in this paper: 1) An improved disturbance observer based (DOB) ISMC strategy is designed to cope with the unknown mismatched disturbances, and the composite nonlinear feedback (CNF) technique is employed in the nominal part of the controller to restrain overshoots and remove steady-state errors considering the tire force saturations; 2) An adaptive super-twisting control (STC) approach is proposed to deal with the disturbances with unknown boundaries using a continuous controller while eliminating the chattering effects. The system stability and robustness are proved via Lyapunov approach. CarSim-Simulink simulation has verified the effectiveness of the proposed control approach in the steering fault case.