Road feeling of electric power steering system based on mixed H₂/H_∞ control

In view of the existence of uncertainties such as system model and disturbance signal in the electric power steering (EPS) system, and the demand for system dynamic performance, the mixed H₂/H_∞ controller is proposed. For the driver to obtain a good steering feeling and for the system to have good robustness and small torque fluctuation, the models of EPS system and the two-freedom car are set up, and the state space model and augmented matrixes are built. The H_∞ method is introduced to minimize the effect of disturbances on outputs, and the H₂ method is applied to optimizing the system performance. The simulation results of steering feeling show that the controller, which synthesizes the advantage of H₂ control and H_∞ control, has better robust performance and robust stability. The controller can attenuate the noises and disturbances caused by road random motivation, torque sensor measurement and model parameter uncertainty, and enable the driver to obtain a satisfactory road feeling.