L1 based control of an active suspension

An active suspension control system design for a tractor-semitrailer transport vehicle is discussed. The design aims at a small L₁-norm of the generalized plant. To-be-controlled signal specifications, related to driver and cargo comfort, limitations of the suspension, driving safety, and road damage, are translated in weighting transfer functions and incorporated in the generalized plant. Due to properties of the generalized plant it is known that an l₁ -optimal controller exists, but not if this controller is a real rational transfer function. Therefore a fixed-structure, fixed-order control synthesis method is employed, that will only generate suboptimal controllers. Design for a single load condition is not satisfactory. Two different approaches to assure robustness are followed: (1) adding an H _∞, or better μ, stability constraint, (2) adding an H₂-constraint for another load condition. Both approaches give acceptable closed loop behavior. To compute controllers, use is made of a Multiobjective Control Design toolbox