Closed-Loop Wake Meandering Control of Downstream Wind Turbines

Enhancing the time-varying meandering effect using phase synchronisation

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Abstract

The offshore wind energy sector has experienced remarkable growth in recent years, driven by increasing demand for renewable energy sources and technological advancements. As wind farms expand and turbine sizes increase, challenges associated with wake effects and turbine interactions become more pronounced. Therefore, wind farm control strategies have been developed to mitigate the negative effects of wakes, consequently enhancing overall power production or reducing fatigue loads. The helix approach has emerged as a promising method for controlling wake dynamics, shaping the wake into a helical pattern to increase wake mixing further downstream.
In this context, phase synchronisation has emerged as an extension of the helix approach, simultaneously applying the helix on up- and downstream turbines. By leveraging the existing helical periodic components induced by the upstream turbine, phase synchronisation can initiate the helix at the downstream turbine with less pitch action. % while improving overall power performance.
However, power is still compromised at the upstream turbine due to the execution of the helix. Consequently, the potential for improvement arises with the integration of phase synchronisation onto the meandering effect—a phenomenon often already present at the downstream turbine. This effect yields benefits similar to those of the helical wake concerning wake recovery, offering the potential to improve overall power performance without power loss at the upstream turbine.
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This thesis has developed a phase synchronisation method to track the time-varying excitation frequency inherent to the meandering effect. Enhancements were made to a SOGI-PLL, enabling the extraction of phase, amplitude, and bias from periodic loads, which forms the basis of our closed-loop control strategy for the downstream wind turbine. The improvements led to the development of the ESOGI- and MSTOGI-HTan-QT2PLL methodologies, which address internal disturbances caused by offsets and enhance system stability, while accurately tracking of the phase during phase jumps and frequency steps and ramps.
The methodologies were tested at different levels of fidelity. First, a low-order study validated the effectiveness of the proposed method during uncertain conditions, which showed better performance of the MSTOGI-HTan-QT2PLL methodology. Then, the results of the higher-fidelity experiments demonstrated that our method could successfully amplify the meandering effect without loss in power, while attenuation led to reduced fatigue loads with minimal power loss. These results show the potential of integrating phase synchronisation on the meandering effect.