The control during the partial load operation, also known as the control in Region II, takes place when the wind speed varies between the cut-in and rated values. In such a case, the wind speed is appropriate to produce power but insufficient to reach the rated power specification. The control objective for variable-speed machines is then to maximize the extracted energy by manipulating the generator electromagnetic torque with values, which are obtained from a maximum power point tracking (MPPT) algorithm. However, an unsmoothed power output as well as the mechanical fatigue in the drivetrain are associated problems. The present chapter presents the most com-mon MPPT algorithms, their problems and ways to overcome them. Moreover, the transition Regions I1/2 and II1/2 as well as the peak shaving control (PSC) are included in the study.
