| A real-time Wind Turbine Emulator (WTE) was developed and constructed that is capable of reproducing the dynamic torque of an actual wind turbine. This emulator models the torque oscillations caused by wind shear, tower shadow, inertia, shaft dynamics and the obvious pulsations caused by variable wind speed. A comprehensive, yet pragmatic model of aerodynamic torque, including the effects of tower shadow and wind shear, was analytically formulated for use in the WTE. The model proves the existence of wind shear induced, blade dependent oscillations and demonstrates that in practice, their presence is masked by the much larger tower shadow induced oscillations. Tower shadow and wind shear cause generator torque oscillations, at multiples of 3 three times the rotor frequency. These and stochastic oscillations, caused by the varying wind speed, are attenuated by addition of the large turbine inertia and to an even greater extent by the flexible shaft dynamics. |
