A new control strategy to suppress the tower vibrations of variable speed wind turbines

Abstract

In this paper, an adaptive internal model based controller is presented for suppressing the tower vibrations in variable speed wind turbines. Wind turbines have a dedicated current and power control module for the second operation region of the machine, where the machine works below the rated wind speed, and a pitch controller for the third operation region of the machine, where the machine works above the rated wind speed. The current and power controllers are designed to maximize the captured power below the rated wind speed, whereas the pitch controller is designed to limit the rotation speed and generated power above the rated wind speed. The pitch controller can further be used to suppress the mechanical tower vibration. Since the vibration frequencies of a tower are not exactly specified in the real turbines, the proposed method, which is based on the behavior of an internal model in an error feedback system, utilizes an algorithm to identify the vibration frequency followed by cancelling the vibration signal. Four different software packages including FAST, TurbSim, AeroDyn, and Simulink are integrated and used for simulation studies. Furthermore, performance of the controller is investigated in normal and fault ride through conditions. The results indicate accurate and proper performance of the controller in terms of identification of the tower vibration frequency and its suppression.