Performance improvement of grid-connected wound rotor induction generators

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 output current and control range is also limited. In the proposed scheme both the voltage control and slip control are employed. Two schemes are presented. Scheme-I is used for maximizing efficiency. An optimum voltage and slip control by rotor resistance is applied such that the efficiency is maximized at every operating point. The scheme-II is used for maximizing power factor. A reduced and constant optimum voltage is applied throughout the range of control. The rotor resistance is varied to operate it at desired slip for optimum power-factor. Here power-factor hence the reactive power demand remains nearly constant throughout the range of operation. These schemes are very useful for wind power based generation where wind speed varies over wide range as well as abruptly