A Methodology for Robust Load Reduction in Wind Turbine Blades Using Flow Control Devices

Abstract

Decades of wind turbine research, development and installation have demonstrated reductions in levelized cost of energy (LCOE) resulting from turbines with larger rotor diameters and increased hub heights. Further reductions in LCOE by up-scaling turbine size can be challenged by practical limitations such as the square-cube law: where the power scales with the square of the blade length and the added mass scales with the volume (the cube). Active blade load control can disrupt this trend, allowing longer blades with less mass. This paper presents the details of the development of a robust load control system to reduce blade fatigue loads. The control system, which we coined sectional lift control or SLC, uses a lift actuator model to emulate an active flow control device. The main contributions of this paper are: (1) Methodology for SLC design to reduce dynamic blade root moments in a neighborhood of the rotor angular frequency (1P). (2) Analysis and numerical evidence supporting the use of a single robust SLC for all wind speeds, without the need for scheduling on wind speed or readily available measurements such as collective pitch or generator angular speed. (3) Intuition and numerical evidence to demonstrate that the SLC and the turbine controller do not interact. (4) Evaluation of the SLC using a full suite of fatigue and turbine performance metrics.

Design of a 3.4‐MW wind turbine with integrated plasma actuator‐based load control

“…If the turbine loads violate constraints (design requirements) that are set, the turbine structural design and baseline controller are refined in coordination until the loads are within acceptable limits. Next, the sectional lift controller (SLC) for the turbine model from Gupta et al 23 is implemented where the SLC is designed to reduce fatigue loading on the turbine without affecting power production or pitch actuator activity. Details of this controller and its design framework are published in Gupta et al 23 In this step, we also introduce a new method we call "active load control emulation (ALCE)."…”

“…Next, the sectional lift controller (SLC) for the turbine model from Gupta et al 23 is implemented where the SLC is designed to reduce fatigue loading on the turbine without affecting power production or pitch actuator activity. Details of this controller and its design framework are published in Gupta et al 23 In this step, we also introduce a new method we call "active load control emulation (ALCE)." ALCE is used to emulate the effect of active load control in the design iterations to evaluate the potential blade mass savings in the wind turbine blade due to a reduction in fatigue loads.…”

“…Thus, OpenFAST enables coupled nonlinear simulation of the complete wind turbine. The custom environment for running OpenFAST simulation in MATLAB and SIMULINK was developed in-house to provide the flexibility to implement the sectional lift controller (SLC) 23 controller as well as to maintain portability between the design and control teams. The tuning process carried out for the generator and pitch controllers is briefly discussed below.…”

“…The resulting turbine with the GF's is the starting point of the implementation of the sectional lift controller (SLC). The SLC design is discussed in detail in Gupta et al 23…”

“…The active load control system in our wind turbine design is from Gupta et al 23 In this reference, the load controller is coined sectional lift controller (SLC) because the DBD plasma actuator (as well as other flow control devices) modulates the lift force along the blade span to reduce blade-root moments. The design process for the SLC, the SLC architecture and parameters, the load reduction performance and the lack of any adverse impact on power production and pitch actuator activity are reported in Gupta et al, 23 which the reader is referred to for full design and analysis methodology of the SLC.…”