A robust controller design for drive by wire hydraulic power steering system

In this paper, a sliding mode controller cascaded by the frequency shaped optimal controller for drive by wire hydraulic power steering system utilizing sliding mode and exponentially convergent observers is presented. Using the robustness implications of the sliding mode control theory and the structural properties of the hydraulic power steering system, a nonlinear controller cascaded by an optimal linear controller is designed to stabilize the steering system dynamics and track the steering wheel reference. Lyapunov based controller design satisfies strong robustness with respect to bounded modeling and parameter uncertainties. The controller and the observer are based on an eight-order nonlinear state-space model of the hydraulic power steering system which is developed, validated numerically with experimental data. Simulation results are included to demonstrate the effectiveness of the observer and the performance of the tracking controller.