Hierarchical Extension H2/H∞ Control Methodology for Active Front Wheel Steering System of Emergency Rescue Vehicle

Abstract Aiming at improving the handling stability of the emergency rescue vehicle (ERV), this paper proposes the hierarchical extension H2/H∞ control strategy into investigating the active front wheel steering (AFS) system of the ERV. Considering uncertainties and the vehicle handling stability, mixed H2/H∞ control method is presented to generate the additional front wheel angle through tracking desired vehicle yaw rate in the upper level. Furthermore, in order to enhance the H2/H∞ control effect, the novel extension control is proposed to change the H2/H∞ control signal dynamically according to different domains defined by the vehicle states. To track front wheel angle from the upper level, this study puts forward the fractional order proportional-integral-derivative (FOPID) controller based on the electro-hydraulic proportional control strategy. The simulations and hardware-in-the-loop experiments are performed to demonstrate the hierarchical control theory. The test results indicate that: (1) the lower level FOPID control method performs better than the PID control on the term of the transient and tracking ability; (2) the hierarchical extension H2/H∞ control strategy proposed ameliorate the vehicle cornering stability well, as well as can make the ERV have better handling stability than conventional H2/H∞ control.