Parametric Analysis for Robust Force/Torque Tracking Control of a Virtual Stiffness-Damping System in Aeroelastic Instability Testing

The force/torque tracking control of a virtual stiffness-damping system (VSDS) for aeroelastic instability testing (AIT) 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 non-AIT fields. However, adaptation of existing VSDSs for use in AIT results in an increased sensitivity to transmission power-loss caused by generally unknown inputs including friction as well as other unmodeled 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 DIE-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 between standard LQG tracking control and the DIE-LQG scheme. Superior performance of the VSDS under the systematically synthesized DIE-LQG control was confirmed.