Multiobjective QFT control as enabler for wind turbines with soft-soft towers

Wind energy tendency towards larger rotors and higher hub heights reach a limit when wind turbine pitch controller bandwidth is constrained by the first tower fore-aft bending moment. While most manufacturers try to find a workaround with alternative nonstandard tower designs, this paper presents a control solution based on quantitative feedback theory (QFT) that provides effective disturbance rejection while maintaining cost-effective conventional tower design for very high hub heights. Frequency domain specifications on measured and nonmeasured variables provide the control designer the insight to make the best use of the available feedback. The new control design procedure is applied to a realistic wind turbine example of 180-m hub height, showing the technical viability of the solution and a profitable business case.