Multivariable Robust Blade Pitch Control Design to Reject Periodic Loads on Wind Turbines

Large-scale wind turbines usually operate in turbulent wind fields. During turbine operation, periodic loads on blades are induced by wind shear, tower shadow effects and centrifugal forces. While collective pitch control (CPC) is unable to deal with periodic loads, the advent of individual pitch control (IPC) provides opportunities to mitigate periodic loads. Nevertheless, difficulties in algorithm development remain. Most notably, wind turbine dynamics is highly nonlinear, and significant modeling uncertainties exist when the turbine operates away from the nominal operation point from which the linearized model is drawn. This paper presents a robust individual pitch control framework to reject periodic loads under model uncertainties. The multi-blade coordinate (MBC) transformation is employed to enable more accurate nominal model development. The turbine model includes horizontal and vertical shear disturbance components in addition to horizontal disturbance. The multivariable individual controller can reduce response peaks at high harmonic frequencies, and the coupling dynamics of three-bladed system is taken into account. The structured singular values ( )-synthesis approach is utilized to guarantee the robust stability and robust performance with respect to uncertainties. Case studies illustrate significant periodic load mitigation as well as fatigue alleviation in speed-varying wind fields.

Journal article