A method for controller parameter estimation based on perturbations

Simulation and prediction of eigenfrequencies and mode shapes for active flexible multibody systems is an important task in disciplines such as robotics and aerospace engineering. A challenge is to accurately include both controller effects and flexible body dynamics in a multidisciplinary system model appropriate for modal analysis. A method for performing modal analyses of such systems in a finite element environment was recently developed by the authors. On issue is, however, that for engineers working in a finite element environment, the controller properties are not always explicitly available prior to modal analyses. The authors encountered this problem when working with the design of a particular offshore windmill. The controller for the windmill was delivered in the form of a dynamic link library (dll) from a third party provider, and when performing virtual testing of the windmill design, it was of great importance to use the “real” controller in the form of the provided dll, rather than re-model it in for instance Simulink or EASY5. This paper presents a method for estimating the controller parameters of PID-type controllers when solving the closed-loop eigenvalue problem for active flexible multibody systems in a finite element environment. The method is based on applying incremental changes, perturbations, to relevant system variables while recording reactions from other system variables. In this work, the theory of the method is derived and the method is tested through several numerical examples.