Robust steer-by-wire control based on the model regulator

Unsymmetrical loading on a car (like μ-split braking, side wind forces or unilateral loss of tire pressure) result in unexpected yaw disturbances that require yaw stabilization either by the driver or by an automatic driver assist system. The use of the two degree of freedom control architecture known as the model regulator is investigated here as a robust steering controller for such yaw stabilization tasks in a driver-assist system. Robust controller design for satisfying a mixed sensitivity constraint is presented. The technique of mapping frequency domain bounds to parameter space is used in the design calculations and explicit formulas for the point condition solution are obtained for the steering model regulator. Design and subsequent simulation studies are conducted at six exemplary operating conditions. While linear simulation results based on the linearized single track model are given, the nonlinear single track model based simulation results are also given to demonstrate the fulfillment of the desired control tasks of yaw moment disturbance rejection and model regulation. The nonlinear single track model simulations are also used to demonstrate the effectiveness of the gain scheduled implementation of the steering model regulator used.