Field testing a wind turbine drivetrain/tower damper using advanced design and validation techniques

As an ongoing trend, the design of wind turbines is moving towards larger machines with components optimized for cost effectiveness. This leads to very large and flexible structures with lightly damped modes. Good control design is becoming more essential to ensure safe and stable operation over the life of the turbine. Additionally, there is growing interest in expanding the number of sensors and actuators available for closed-loop control. The increasing number of control variables in modern wind turbines will necessitate model-based controller design to handle the complexity of the flexible and coupled control loops in an effective and robust way. Recent literature in wind energy has explored the use of modern control design techniques such as state-space and robust control design methods and closed-loop system identification for model identification. However, this literature is, to date, mostly confined to simulation studies. Field testing is necessary to demonstrate the effectiveness of advanced design and validation techniques in a practical application. In this paper, we design two alternative dampers for the lightly damped drivetrain and tower modes of an experimental turbine. One design is based on classical iterative design approaches, while the other uses an H_∞ approach. The two controllers are then validated using two alternative methods: the traditional extended field test and a relatively short system identification experiment. The paper demonstrates that even in this sub-problem of wind turbine control consisting of only two loops, the use of advanced design and validation techniques is very effective at converging quickly to good control designs and quickly assessing their performance.