Offset-Free Predictive Control for Variable Speed Wind Turbines

Wind turbine aerodynamics is known as a nonlinear and stochastic system; hence, a high-performance requirement of tight optimal regime tracking is beyond the capability of the conventional linear PI controller. On the other hand, the linear model of the nonlinear wind turbine aerodynamics at a specific operating point produces a mismatch between plant and model which is the main reason for reference tracking offset seen in a conventional predictive controller. This paper presents a new predictive control approach for variable speed wind turbines in order to guarantee maximum power captured under the rated wind speed. The proposed algorithm, offset-free predictive control (OF-PC), has been exploited to provide zero error tracking of the nonstationary optimal speed trajectory. The control scheme attempts to add additional output disturbance signals to the linear presentation of wind turbine aerodynamics together with an appropriate observer design to lump the plant-model mismatches and/or unmodeled disturbances. The simulation and experiment results demonstrate the effectiveness of the control method.