A New Variable-Speed Wind Energy Conversion System using Double-inverter-fed Wound Rotor Induction Generator

The double-inverter-fed wound rotor induction generator (DI-WRIG) is proposed in this article as a potential candidate for wind energy conversion system (WECS) because of its increased freedom of control, wide speed range and efficient operation. By controlling the frequencies of the supplied voltages to both stator and rotor terminals of the generator, it is possible to operate the DI-WRIG in super-synchronous mode at any shaft speed, enabling efficient operation over the entire speed range. Further, the efficiency of a DI-WRIG can be maximized by appropriate selection of the total magnetizing current, the supply frequencies and the sharing of magnetizing current between stator and rotor, for a given turbine power curve. Design considerations of the proposed DI-WRIG for application in wind energy conversion are discussed. Moreover, an offline approach to derive optimum operating conditions of the generator for a given wind turbine characteristics is presented in this article. Experimental results are presented from a 7.5 kW laboratory-scale WECS prototype to demonstrate the performance of the proposed wind turbine generator.