Wind-driven, variable-speed, variable-frequency, double-output, induction generators

In this paper the performance of a self-excited, wind-driven, variable-speed, variable-frequency, double-output induction generator (VSVF-DOIG) is presented. This Generator will be used to supply frequency insensitive loads such as space heating. For the capacitor-excited machine, the stator frequency varies with the rotor speed, thereby yielding a small value of slip. Thus, the minimum capacitance under load can be approximately predicted in terms of the wind speed. The control methodology is the following. The rotor is short-circuited. As the rotor speed increases, the capacitance is diminished until the stator current, the stator voltage and the voter speed reach their rated values With further increases of the rotor speed, the capacitance, the stator current and the rotor current are held constant and additional power is extracted from the system by adjusting the resistive load in the rotor circuit. Hence this control strategy allows more than rated power to be extracted from the induction machine without overheating it. The theoretical results of this investigation are verified experimentally.