Robust control of 4WS actuator using LMI

The actuator in a 4-wheel steering system must satisfy many control requirements; responsiveness and stability arising from improved vehicle dynamics, robustness against disturbance and noise in the operating environment, reduction of the effects of disparities in component quality, and electric power efficiency. We selected a design method based on the LMI technique in order to satisfy these requirements. This choice was due to the following three reasons: 1) A numerical solution can be obtained to design the controller because the requirements of responsiveness, stability, disturbance suppression and robustness can be managed using mixed H²/H^∞ synthesis with regional pole placement; 2) A LMI-based control design has less limitation than Riccati-based control design. 3) External disturbance, which is dependent on the state quantities of the object of control, can be expressed as a model with polytopic uncertainty. This makes it possible for the controller design to take into account this uncertainty. Based on the above, we decided on an integrator-type optimal regulator incorporating a reference model for the structure of the controller. Control gain design results are described