Robust H2 optimal control of an active suspension

An active suspension control system design for a tractor-semitrailer transport vehicle is discussed. The design aims at optimality of the $\Htwo$-norm of the generalized plant for a large range of semitrailer load conditions. Model parameters are taken from a real vehicle. Specifications for the disturbance input signal accounts for a stochastic road disturbance, but the design verification also considers a class of deterministic ones. 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. A design for a single load condition is not satisfactory. Two different approaches to assure robustness are followed: (1) a simultaneous $\Htwo$ optimal design for two plants, representing two extreme load conditions, (2) adding an $\Hinf$, or better $\mu$, stability constraint. Both designs show acceptable closed loop behavior. To compute controllers, use is made of a Multiobjective Control Design and a Linear Matrix Inequalities toolbox.