Maximum Power and Maximum Power Factor Tracking of Grid Connected Wound Rotor Induction Generators

Abstract

Input voltage control has been used for improvement of power factor in grid-connected induction generators. However, this method reduces the efficiency drastically due to high input current. Moreover the control range is also limited. In the proposed schemes, both voltage control and slip control are employed together to control the efficiency and power factor. Scheme-I is used to tap maximum power from the wind turbines using wound rotor induction generators. It also controls the local bus voltage and maximizes efficiency of the generator. At an optimum voltage, slip control is employed such that the output is maximized at every operating point. The scheme-II is used for maximizing the power factor. An optimum grid voltage is applied to the generator and the effective rotor resistance is varied to operate it at desired slip for the optimum power-factor. Here the power-factor hence the reactive power demand remains nearly constant throughout the range of speed variation. These schemes are very useful for wind based power generation where wind speed varies abruptly over wide range. For this purpose personal-computer (PC) based ac regulator is employed. The proposed controllers work satisfactorily even at dynamic conditions.