Model Predictive Control of semi-active and active suspension systems with available road preview

Abstract

Semi-active and active suspensions influencing the vertical dynamics of vehicles enable improvement of ride comfort and handling characteristics compared to vehicles with passive suspensions. If the road height profile in front of the car is measured using vehicle sensors, more efficient control strategies can be applied. First, regarding vehicles with continuously variable dampers: A Model Predictive Controller incorporating the nonlinear constraints of the damper characteristic is set up and compared to a controller using linear constraints. The approximate linear constraints are obtained by a prediction of passive vehicle behavior over the preview horizon using a linearized model. Additionally, a controller without input constraints and clipping of the damper force is applied. This results in a quadratic program without constraints, which can be solved efficiently. The result of applying the optimal force without constraints is also evaluated, which corresponds to an ideal high bandwidth actuator. Next, two controllers for vehicles with a low bandwidth active suspension and variable dampers are proposed. While the first approach optimizes only the actuator displacement combined with the damper's soft characteristic, the second approach optimizes both the damper force and the actuator displacement. Simulation results of the controllers and the active and semi-active suspensions over real road height profiles are presented.