Due to the increased share of (offshore) wind turbines, more stringent power requirements have been established. Importantly, the low-voltage ride-through requirement states that a wind turbine must remain connected to the electrical grid after a short intermittent grid fault. In the industry and academia many solutions have been proposed, but these are limited by requirements of detailed system knowledge, lack of optimality guarantees, or no testing on high-fidelity models. Therefore, two Iterative Learning Control (ILC) algorithms are presented aimed to solve these issues. The ILC algorithms apply model-free learning based on iterations. Shown is that these ILC algorithms can yield improved performance on a low- and high-fidelity models, with fast convergence of the 2-norm of the output error. The major contributions of this work lie in the application of ILC on grid fault control for wind turbines and in the extension of the norm-optimal ILC to include input constraints using optimisation methods.

Pressure sores are a major problem for spinal cord injured (SCI) patients. Prevention should be directed towards diminishing both intrinsic and extrinsic risk factors. Extrinsic factors such as pressure and shear forces, exerted over time, can be minimized by use of an inflatable wheelchair cushion. Reduction in body-seat interface pressure is, however, influenced by the inflation pressure. The time factor can be influenced by changes in position. In the present study the effect of inflation pressure and body tilt on body-seat interface pressure was measured in 18 SCI patients, sitting on a Roho cushion in a wheelchair with an inclinable seat. Measurements were performed at inflation pressures of 20, 30 and 40 mm Hg, and seat inclinations of 5°, 15° and 25° from the horizontal. A statistically significant effect of both inflation pressure and body tilt was found. An inflation pressure of 20 mm Hg yielded the lowest interface pressures, as did a body tilt of 25°. Due to considerable inter- and intra patient variation the use of body-seat interface measurements to define an optimal seating condition in the clinical situation, remains limited.