Performance of Linear Control Methods for Wind Turbines Dealing With Unmodeled Structural Modes

Wind turbines commonly operate in an uncertain and noisy environment. Disturbance accommodating controller (DAC) has shown promising results in dealing with changing wind speed to regulate generator speed at its rated speed in above rated wind speed condition. However, it has been reported that the number of considered system modes (or degrees of freedom) in design of DAC affects the system performance. Simulation using high order model, higher than that is considered in the control design, showed unstable response due to effect from the unmodeled structural dynamics. In this study, DAC with Kalman estimator is designed for variable pitch wind turbines to take into account the unmodeled dynamics and noise measurement. The control performance is simulated using high order FAST model that has active generator, drive-train, blade, and tower dynamics in Simulink environment. Simulation results show that DAC with Kalman estimator gives best performance in terms of speed regulation and control cost, compared to two other linear controllers: Gain Scheduled Proportional Integral (GSPI) controller and DAC with linear estimator.