Backstepping based fuzzy logic control of active vehicle suspension systems

In this paper, we present a backstepping based fuzzy logic (FL) scheme for the active control of vehicle suspension systems using the two-degrees of freedom or 1/4 car model. The full dynamics of a novel hydraulic strut are considered. The servo-valve dynamics are also included. A fuzzy logic system is used to estimate the nonlinear hydraulic strut dynamics. The backstepping fuzzy logic scheme is shown to give superior performance over passive suspension and active suspension control using conventional proportional-integral-derivative (PID) schemes. The FL system is adapted in such a way as to estimate online the unknown hydraulic dynamics and provide the backstepping loop with the desired servo-valve positioning so that the scheme becomes adaptive, guaranteeing bounded tracking errors and parameter estimates. A rigorous proof of stability and performance is given and a simulation example verifies performance. Unlike standard adaptive backstepping techniques, no linear-in-the-parameters assumptions are needed.