Linear robust control for a nonlinear active suspension model considering variable payload

The control of active suspension systems is described in many publications over the last decades. However, often only idealized linear models are used for control design and simulations, what can lead to wrong conclusions regarding controller performance and energy costs. Therefore, this paper presents a nonlinear passive suspension model of a quarter car test-rig currently built up at the Institute of Automatic Control which can be extended with models of active elements. Furthermore it is lined out, how a robust controller can be synthesized for this system. For this purpose the nonlinear model is linearized around the equilibrium point and parametric model uncertainties are introduced together with performance weighting functions. In order to include the influence of the variable chassis payload into the design process, a trim point uncertainty is added which completes the structured uncertainty model. With this a modern robust control design approach using the structured singular value can be presented, considering different chassis masses and their influence on the linearization point. Finally it is demonstrated, how robust performance or robust stability can be analyzed if a linear controller already exists.