Comparison of Down-Regulation Strategies for Wind Farm Control and their Effects on Fatigue Loads

Abstract

With the growth of wind energy worldwide, an increased interest in wind farm control has become visible, with Active Power Control (APC) and Active Wake Control (AWC) being two primary examples. Both these methods rely on the down-regulation (i.e., operation using sub-optimal power settings) of wind turbines in order to provide such services. Apart from these services, down-regulation also affects the loads acting on a wind turbine. Hence, it is important to analyze the effects on the lifetime of wind turbine components, e.g., the tower, blades and rotor shaft. Earlier research on APC for wind farms has resulted in several down-regulation methods which were shown to reduce fatigue loads for some wind turbine components. One of these methods is called the percentage reserve method, which makes it possible for the wind turbine to generate a desired percentage of the available power at every wind speed. In this paper, different down-regulation strategies using the percentage reserve method are assessed on their capability of reducing fatigue loads. The performance of the different control strategies is compared using aeroelastic simulations and by comparing the Damage Equivalent Loads (DELs) of several components for the whole range of operational wind speeds. The fatigue lifetime is analyzed by combining the DELs with a wind speed distribution for the turbine specific wind class. The results show that all down-regulation strategies are capable of achieving significant lifetime fatigue load reductions for some wind turbine components. Whichever strategy provides the best performance, depends on the user's wishes as well as the environmental conditions and the wind turbine in question.

Managing Wind Turbine Generators with a Profit Maximized Approach

“…Forecasting of the RUL thus represents a crucial element in order to establish a commercial optimal replacement strategy and to execute additional investments in WTG with at least 15 years of operation with minimal risks. Derating is seen as the most promising concept to increase RUL by [17] and [18], while [19] combines derating and individual blade control to further increase the RUL. According to [1], the failure of all main components of a WTG-except the yaw system-is impacted by high wind speeds and high wind speed variability.…”

On Wind Turbine Power Delta Control

“…Other authors have proposed a simple extension to the modified MPPT curve, to achieve proportional delta control via a combination of generator speed and blade pitch angle modifications [14]. This allows precise control of the tip-speed ratio λ and the blade pitch angle β at different de-rating command values, which is relevant to turbine dynamics and loads [14][15][16][17]. Its implementation is rather simple, as shown by Figures 1 and 2, where the two black 1D look-up tables are sufficient.…”

“…Note that solutions of (33) are generally non-unique, which leaves one degree of freedom for the choice of λ δ and β δ on the basis of criteria other than those discussed here (see, for example, [15]). Figure 7 shows two different {k δ , β δ } trajectories, over the Cp (λ, β) contour plots of two popular reference turbines (note that the one on the right coincides exactly with Strategy 3 in [15]). The resulting k δ (δ) and β δ (δ) look-up tables are shown by Figures 8 and 9, respectively.…”

“…Repeating for different values of δ or P δ , these vectors become matrices, and the 2D look-up tables giving β δ (Q e , δ) and β δ (ω, δ) or β δ (Q e , P δ ) and β δ (ω, P δ ) are ready. Figures 10,11,15,and 16 show said tables for two popular reference turbines.…”

“…Calculate the k δ 2b 3 P δ ρπR ω 3 and β δ 2b 3 P δ ρπR 5 ω 3 look-up tables. 1:Choose a tip-speed ratio λ δ and a pitch angle β δ (for example, as in[15]).…”