In the pursuit of cleaner energy, wind turbines are growing in size, promising higher power output but also presenting unique design challenges. As blades become larger and more flexible, their aerodynamic performance and loading under varying conditions become increasingly complex. A recent study published in the journal *Wind Energy Science*, titled “COFLEX: a novel set point optimiser and feedforward–feedback control scheme for large, flexible wind turbines,” addresses these issues head-on. The research, led by Dr. Gabriele Lazzerini from the Delft Center for Systems and Control at Delft University of Technology, introduces a novel control strategy that could redefine the future of wind turbine design and operation.
Traditional control strategies, such as tip-speed ratio tracking, aim to maximize power production by maintaining a constant ratio between blade velocity and wind speed. However, these approaches falter when faced with large blade deformations, where deflection and structural twist significantly impact aerodynamic performance. “The current state-of-the-art control strategies do not fully account for the effects of blade flexibility on aerodynamic response,” explains Dr. Lazzerini. “This oversight can lead to suboptimal power production and increased structural loads.”
To address this gap, Dr. Lazzerini and his team developed the COntrol scheme for FLEXible wind turbines (COFLEX). This innovative feedforward–feedback control scheme leverages optimal operational set points computed by COFLEXOpt, a set point optimiser that considers the effects of blade deformations on aerodynamic performance and turbine loading. “COFLEXOpt provides controller set points while allowing constraints to be imposed on various operational, structural, and load properties, such as blade deflection,” says Dr. Lazzerini.
The COFLEX strategy consists of two key modules. The first, COFLEXOpt, is an optimisation framework that generates set points agnostic to operating regions, meaning the operating region boundaries are optimised rather than prescribed. The second module is a feedforward–feedback controller that uses the set point mappings generated with COFLEXOpt to evaluate feedforward inputs and provide feedback to correct modelling inaccuracies and ensure closed-loop stability. A set point smoothing technique enables smooth transitions from partial- to full-load operations.
The researchers tested the effectiveness of COFLEX using the IEA 15 MW turbine as a case study. Their analysis showed that accounting for blade flexibility leads to variable optimal tip-speed ratio operating points in the partial-load region. The collective pitch angle can be used to counteract blade torsion, maximizing power coefficient while complying with imposed constraints. Time-marching mid-fidelity HAWC2 simulations across the entire operational range of the IEA 15 MW reference wind turbine demonstrated excellent agreement between optimised steady states and median values obtained from simulations. Moreover, the generator power showed an increase of up to 5% in the partial-load region compared to the reference scheme while maintaining blade deflection at a similar level.
The implications of this research for the energy sector are substantial. As wind turbines continue to grow in size, the ability to optimize power production while minimizing structural loads will become increasingly important. COFLEX offers a promising solution to these challenges, potentially leading to more efficient and cost-effective wind energy generation.
Dr. Lazzerini’s work not only advances our understanding of wind turbine control but also paves the way for future developments in the field. As the world continues to transition towards renewable energy, innovations like COFLEX will play a crucial role in maximizing the potential of wind power. “This research is a significant step forward in the quest for more efficient and reliable wind energy,” says Dr. Lazzerini. “We hope that our findings will inspire further advancements in the field and contribute to a more sustainable energy future.”