A novel robust <i>H</i> ₂ <i>/H</i> ∞ control for 4WS vehicles considering closed-loop regional pole constrained

In order to address the problem of system performance degradation due to the presence of time-varying parameters and external perturbations in a four-wheel steering (4WS) vehicle system, an H 2 /H ∞ robust controller considering closed loop regional pole constraints is proposed. Firstly, H ∞ control is used to reduce the effect of modeling errors and external perturbations on the 4WS system. H 2 control is used to ensure the performance of the 4WS system. Considering the closed loop regional pole constraints to configure the system poles into a given region, the controller achieves satisfactory transient performance even if the system is subject to parameter variations and perturbations external to the 4WS system. Secondly, a novel stability envelope method is considered to determine the stability envelope region of a 4WS vehicle. Subsequently, a trajectory tracking controller based on H ∞ control is designed to validate the handling stability and steering flexibility of 4WS vehicles. Finally, some simulation scenarios are given to demonstrate the effectiveness of the proposed method. The results show that the H 2 /H ∞ controller outperforms the front wheel angle proportional feedback control even when the vehicle mass, front tire cornering stiffness, and rear tire cornering stiffness are greater than 30% of the design criteria values of the 4WS vehicle controller. In the simulation and hardware-in-theloop experiment (HIL) results of the H ∞ trajectory tracking controller, it is demonstrated that the H 2 /H ∞ controlled 4WS vehicle improves the trajectory tracking accuracy and handling stability of the vehicle.