Parametric analysis for robust force/torque tracking control of a virtual stiffness-damping system in airfoil aeroelasticity testing

Abstract

The force/torque tracking control of a virtual stiffness-damping system (VSDS) for airfoil aeroelasticity testing is studied in this paper. Existing test-beds rely on elastic elements or structures to set airfoil elasticity in tests, which can be costly and inconvenient in cases of frequent stiffness adjustment across a wide range. A possible alternative is the VSDS that utilizes electric drives to simulate the effects of structural elasticity and damping, as seen in marine and biomechanics engineering. However, the potential VSDS for airfoil aeroelasticity testing is more prone to transmission powerloss caused by generally unknown inputs including frictions as well as other un-modeled dynamics and disturbances, due to different operation principle and conditions compared with other existing VSDSs. This is a critical problem that can result in inaccurate virtual stiffness and damping. In this paper we tackle this problem by treating power loss as an unknown input and employing the linear-quadratic-Gaussian (LQG) tracking control enhanced by unknown-input estimation (UIE). A systematic procedure based on numerical study is proposed to investigate the effects of UIE-related parameters on system sensitivity and stability robustness. To confront uncertainties in parametric analysis, a stability robustness index is proposed. Findings from the proposed parametric analysis not only assist effective controller design but also correct and supplement the existing knowledge in literature. Wind-tunnel experiments were conducted with comparisons drawn between standard LQG tracking control and the UIE-LQG scheme, and satisfactory performance of the VSDS under the systematically synthesized UIE-LQG control was confirmed.