Robust H∞-based vehicle steering control design

Two vehicle steering controllers to improve the yaw dynamics of a mid-size passenger car are designed based on robust H∞ synthesis techniques. The controllers fulfill the desired mixed-sensitivity performance specifications robustly with respect to large uncertainties in the vehicle model parameters for longitudinal speed, road adhesion, mass and moment of inertia. The parametric uncertainties are non-conservatively considered using a minimal-order linear fractional representation (LFR) for the uncertain vehicle model during control design. One approach is based on μ-synthesis, which guarantees robust performance assuming that parameters are uncertain but constant. The second design is based on linear parameter varying (LPV) control design techniques, guaranteeing robust performance also in case of bounded variation rates of the longitudinal speed, which is an important property in real-life situations like μ-split braking. To allow real-time implementation, frequency weighted controller reduction techniques are applied to reduce the order and to eliminate high frequency dynamics of the controllers.