LPV control with decoupling performance of 4WS vehicles under velocity-varying motion

In this paper, a new control strategy with robustness for four-wheel steering vehicles is proposed, which has the decoupling performance while vehicles are steering with varying velocity. To get velocity-varying model, it is considered for the first time, that longitudinal velocity as a state and output is decoupled with lateral velocity and yaw rate while the driving force is taken as the control input in the longitudinal subsystem. Based on this completed decoupling result, the subsystem with lateral velocity and yaw rate as states is transferred into a typical linear-parameter varying (LPV) system for the first time, where varying parameters are longitudinal velocity and its functions. Then to this LPV system, lateral velocity and yaw rate are decoupled into lower triangular structure with steering angles using a suitable distribution coefficient of total longitudinal force while the cornering stiffness coefficients are considered as uncertain parameters. To improve the robustness of the above decoupled system, a new LPV controller is designed at last. In this new control strategy, feedback signals are longitudinal velocity, the yaw rate and lateral velocity. However, lateral velocity need not be designed the observer or measured precisely. Simulation results show that, even though with a large velocity-varying range, the handling characteristics, safety and comfort of the vehicle driving are improved significantly.