The generator efficiency, defined in Eq. (29), is presented in Fig. 13. Strategies A–C lead to similar generator efficiencies, the two major trends being that increased average wind speed causes a higher generator efficiency while a higher frequency of the wind speed reduces the generator efficiency. In the high wind speed case at low frequencies, the generator efficiency of the reference strategy is similar to that of the other strategies. However, the generator efficiency with the reference strategy is lower at high wind frequencies. This reduced efficiency is due to high resistive loss caused by the high generator torque during the rapid oscillations. In the low wind speed case at wind frequencies of 0.01–0.03 Hz, the generator efficiency is higher with the reference strategy than with the other strategies, since strategies A–C operate at too high rotational velocities and thereby increase the already dominant core loss. In the low wind speed case at wind frequencies above 0.003 Hz, the reference strategy causes a too low average tip speed ratio which reduces energy capture, see Figs. 10 and 11.
major trends
two
wind
frequencies
0.01–0.03 Hz
Hz
wind
frequencies
above 0.003 Hz
Hz