Controls of a flywheel in a wind turbine rotor

In this article, the control strategy for a previously proposed flywheel system that is integrated in a wind turbine rotor is presented. This control strategy allows the flywheel system to serve two purposes: support of the frequency in the grid and mechanical load mitigation in the wind turbine. For the first purpose, extra energy is fed into the grid whenever there is a contingency; alternatively, the varying power output from the wind turbine can be stabilized. For the latter purpose, the flywheel is applied to detune the eigenfrequency of the most vibratory components in a wind turbine, that is, the rotor blades. Simulations are shown to illustrate the principle and the performance of the proposed system. It is concluded that the controls of the flywheel system manage to support the grid frequency and also mitigate mechanical vibrations in different operating points of the wind turbine.