l1-Optimal Control of Large Wind Turbines

We present an l(1)-control scheme for multivariable pitch control in full load region. Two decoupled linear time-invariant models are derived using Coleman transformation and gain scheduling to design collective and individual pitch controllers independently. Individual pitch control is used to decrease the blade root bending moment. A new l(1)-control setup for collective pitch control taking into account the collective bending moment in Coleman mode is presented. This further decreases the blade root bending moment while rotor speed is maintained constant above rated wind conditions. Simulations with a full nonlinear aeroelastic model over the whole load region show the applicability of the proposed control strategy and lifetime weighted damage equivalent loads are computed. Compared to classical collective and individual pitch control, a significant load reduction is achieved without losses in energy production.