Improved optimal sliding mode control for a non-linear vehicle active suspension system

The objective of this study is to present an improved optimal sliding mode (SM) control method for non-linear active suspension systems to obtain both the true nominal optimal suspension performance and better robustness. A general non-linear suspension dynamics model is established first. Its non-linear control scheme is applied using the improved optimal SM control method. This non-linear active suspension control system is linearized utilizing the feedforward and feedback linearization method. A fact is theoretically discovered that the general optimal SM control for the linearized active suspension system cannot provide true optimal results. Thus, the improved optimal SM controller for the linearized active suspension is proposed to address the disadvantages of the general optimal SM controller. The improved optimal SM controller is designed by constructing an augmented optimal sliding mode manifold function, which includes all of the information of the structure and expected performance of the suspension. The advantages of the proposed controller are illustrated by comparing the performance of the improved optimal SM control, the fuzzy logical SM control, and the passive suspension. The simulation results verify that the proposed improved optimal SM control achieve the true nominal optimal suspension performance for a non-linear active suspension system in general condition. The results also show that even if the structure parameters and/or running conditions change, the proposed improved optimal SM control can still provide more robust characteristics.