Effects of Disturbance Augmented Control Design for Wind Turbines

The use of disturbance models in wind turbine individual pitch control design to attenuate effects of persistent disturbances is investigated. Previous work has used individual pitch control and disturbance models to design controllers that reduce the blade loads at the frequencies associated with the rotor speed. This paper takes a similar approach of using a disturbance model within the H∞ design framework to account for periodic loading effects. The controller is compared with a baseline design that does not include the periodic disturbance model. In constant wind speeds, the disturbance model design is significantly better than the baseline design at canceling blade loads at the rotor frequencies. However, these load reduction improvements are eliminated even in low turbulent wind conditions well below limitations defined in the commonly used wind turbine design standards. The two controllers perform similarly in turbulent conditions because the turbulent wind contains energy across a broad frequency spectrum. Therefore inclusion of periodic disturbance models in the control design may not lead to the expected load reduction in fielded wind turbines.