$\mathcal{H}_\infty$ Loop-shaping for Power Tracking Control of Wind Turbines

TL;DR

This work addresses the need for accurate active power tracking and maximum power extraction in wind turbines under variable winds, with robustness guarantees. It proposes a two-mode H-infinity loop-shaping controller design (one mode for power maximization and one for power reference tracking) plus a bumpless transfer scheme to switch between modes without transients. Equilibria and linearization around operating points drive the mode-specific controller synthesis, using pre- and post-compensators to shape the loop and achieve offset-free tracking. A case study with OpenFAST demonstrates improved power tracking accuracy, competitive power capture, and favorable robustness and wear characteristics compared to a reference controller, supporting practical deployment in grid-supporting wind farms.

Abstract

In this paper, we present an advanced wind turbine control scheme for power maximization as well as for active power control, which is designed using $\mathcal{H}_\infty$ loop-shaping. Our approach involves the synthesis of two separate controllers for two different operating modes. To ensure smooth transitions between these modes, we implement a bumpless transfer strategy that reduces transient effects. A comprehensive case study demonstrates the efficacy of our control scheme, showing significant improvements in power tracking accuracy and a reduction in mechanical wear. Moreover, our control strategy comes with robust stability guarantees.

Figures (8)

• Figure 1: Operating regions of wind turbine.
• Figure 2: Loop-shaping design approach: Closed-loop $\mathcal{H}_\infty$-control diagram.
• Figure 3: Bumpless switching with $K_2$ and $K_3$ running in parallel.
• Figure 4: Robustness analysis for $K_2$ and $K_3$ indicate an overlapping area (in blue) where both controllers guarantee stability. Note that all operating points lie below the dashed line that represents the physical maximum power that can be harvested at a given wind speed.
• Figure 5: Power maximization below rated wind speed at a mean wind speed of 6.4ms and a turbulence intensity of 7%.