Fault Tolerant Control of an Experimental Flexible Wing

Abstract

Active control techniques are a key factor in today’s aircraft developments to reduce structural loads and thereby enable highly efficient aircraft designs. Likewise, increasing the autonomy of aircraft systems aims to maintain the highest degree of operational performance also in fault scenarios. Motivated by these two aspects, this article describes the design and validation of a fault tolerant gust load alleviation control system on a flexible wing in a wind tunnel. The baseline gust load alleviation controller isolates and damps the weakly damped first wing bending mode. The mode isolation is performed via an H 2 -optimal blending of control inputs and measurement outputs, which allows for the design of a simple single-input single-output controller to actively damp the mode. To handle actuator faults, a control allocation scheme based on quadratic programming is implemented, which distributes the required control energy to the remaining available control surfaces. The control allocation is triggered in fault scenarios by a fault detection scheme developed to monitor the actuators using nullspace based filter design techniques. Finally, the fault tolerant control scheme is verified by wind tunnel experiments.

Advanced Gust Load Alleviation using Dynamic Control Allocation

“…Compared to the open-loop case, however, the WRBM is still reduced since the mid and inner flaps are still in operation. After a fault detection time of a bit more than 1 s, which is reasonable as evaluated in [15], the GLA controller is reconfigured and dynamic control allocation is activated at around 5 s. From thereon, the demanded control effort is distributed to the two inner flaps while the command to the faulty actuator is set to zero. Clearly visible in Fig.…”

“…A similar approach is followed in [14], where the control allocation problem is formulated in terms of a quadratic program instead of a linear program. Note that both dynamic control allocation and MPC do not only allow for effectively handling saturation effects but also actuator faults, see, e.g., [15,16].…”

Performance analysis of control allocation using data‐driven integral quadratic constraints

“…The objective of the quadratic program is to keep both $$$ \delta u $$$ and $$$ \delta \tau $$$ at zero, where dedicated weightings ensure that redistribution is preferred over performance degradation. For more details on the design, tuning, and implementation of the overall gust load alleviation controller see References 6 and 52.…”

“…The control allocation scheme typically exploits the additional degrees of freedom from over-actuation to handle actuator constraints or minimize some performance criteria like energy consumption. This makes control allocation very attractive in various application fields such as road and all-terrain vehicles, [1][2][3] aerospace, [4][5][6] marine vehicles, 7,8 manipulators, 9 or bio-mechanical muscles. 10 However, if the virtual inputs cannot be adequately realized, for example, due to saturation of multiple actuators, closed-loop performance is usually degraded and in the worst case, stability issues may even arise.…”

Identification and assessment of a nonlinear dynamic actuator model for controlling an experimental flexible wing

“…Active load alleviation allows for notable structural mass savings, which will in turn lead to decreased fuel consumption and, thus, lower operating costs and less emissions. The German Aerospace Center (DLR) has investigated the benefits of an active load alleviation system by numerical simulations and by wind tunnel experiments within the internal research activity "KonTeKst" [1][2][3][4]. For the design of a suitable control law, a numerical model of the open-loop system is required.…”