Active Load Control of Wind Turbines Using Plasma Actuation

Wind turbines are progressively moving toward larger rotor diameters, hub heights, and power ratings to lower the Levelized Cost of Energy (LCOE) by increasing the Annual Energy Production (AEP). However, as wind turbines get larger and larger, simply scaling the rotor diameter and rated power comes into conflict with the ‘square-cube law’, where the amount of material used in the blade scales with its volume (the cube), while the energy capture scales with the area of the rotor (the square). Thus, the capital costs can grow faster than the gains in energy production. One approach to disrupt the square-cube law and reduce the LCOE further is to mitigate aerodynamic loads by employing on-blade Active Flow Control (AFC) devices. By reducing aerodynamic loads, with no adverse effects on turbine performance, this approach allows longer blades with less material and, thus, lower capital costs. The research in this dissertation seeks to quantify the performance of plasma-based active load control under different setups and wind conditions. It aims to explore the potential of using plasma-based actuators for active load control through detailed modeling, validation, simulation, and analysis processes. Dielectric Barrier Discharge (DBD) plasma actuators have several advantages over other AFC devices, including having no moving parts, being lightweight, having a high bandwidth response, and being easy to integrate on blades. These devices can be used to modulate the local lift along the blade span. Therefore, the first part of this dissertation research focuses on the modeling and validation of the DBD plasma-based lift actuator. A detailed modeling process of the lift actuator in the NREL FAST simulation tool is presented. The results of a preliminary wind tunnel experimental validation for the lift actuator are also presented and discussed. Then, an investigation of using multiple lift actuators compared to using a single lift actuator on each blade for dynamic load control is conducted. Open-loop and closed-loop feedback control systems are designed to investigate the performance difference between using single and multiple actuators. Next, inspired by a previously published bound on achievable load reduction, parametric and sensitivity studies of typical blade design parameters are carried out to explore and evaluate the use of the bound to better understand the relation between actuator effectiveness and blade geometry. After that, a methodology for designing and evaluating a feedback control system using lift actuators to alleviate the extreme loads under gust wind is proposed. A switching scheme is described to integrate the gust load controller into turbines with an existing dynamic load controller to achieve extreme loads and deflections reduction while maintaining the fatigue load reduction capability. Finally, as wind turbines in the field can be exposed to off-design conditions intentionally or unintentionally, which could adversely affect the wind turbine loading condition and power production, the combined plasma-based fatigue and gust load controller are evaluated under off-design conditions. The performance of the load controller on fatigue loads, turbine performance, and extreme loads is investigated under two off-design conditions—yaw misalignment and blade contamination.