Design of a Non-linear Controller for Vehicle Active Suspension System, Considering Practical Constraints

In this paper two non-linear control strategies were employed to design the controller for vehicle active suspension systems, considering the non-linear dynamics of the hydraulic actuator. At first, a controller is designed using Lyapunov’s method in which the square of the vertical acceleration was chosen as the Lyapunov function. Simulation results indicate that this controller is successful in reducing the vertical acceleration to improve the ride comfort, but it can not control the stability and steerability of the vehicle. Meanwhile, the designed controller is not robust enough to system parameter perturbations. Therefore, the sliding mode control as a robust non-linear control method was adopted as an alternative. In this method, the sliding surfaces were selected in a way that the non-linear system tracks a “sky-hook” model, which has desirable behavior. In order to improve the characteristics of the reference model in terms of ride comfort and steerability, considering the practical constraints of the suspension system, an optimal LQR controller was designed for the sky-hook model. Simulation results show that the controlled system tracks the behavior of this new reference model well. Also, the sliding mode controller is robust to parameter perturbations.