Single-Blade Individual Pitch Control with Phase Compensation for Wind Turbine Periodic Blade Load Reductions

Abstract

As wind turbine sizes and their rated power capacities increase, the spatial and temporal load imbalances over the rotor surface increase due to larger wind asymmetries, aerodynamic imbalances, and calibration offsets. The multiblade coordinate (MBC) transform-based individual pitch control (IPC) has garnered significant attention in the literature, and it considers loads in a non-rotating reference frame. This leads to increased pitch actuation for all wind turbine blades when subject to large load imbalances. On the contrary, the single-blade control (SBC) IPC strategy is well suited for handling such load imbalances as it involves equipping each blade with a localized control system, thereby ensuring an independent operation in a rotating reference frame. However, unlike MBC transform-based IPC, the effects of system phase lag on SBC performance have not been investigated. This article investigates the effects of such phase lags and multivariable coupling on SBC performance, and proposes a novel framework for phase compensation in SBC as a convenient method for constructing and calibrating a lead compensator. Using midfidelity OpenFAST simulations, it is demonstrated that phase compensation in SBC improves load mitigation at the targeted frequencies and reduces actuation effort. In contrast, the absence of phase compensation can lead to load amplifications, especially for larger wind turbines.