Variable-speed variable-frequency（VSVF）， a new typed operational mode for the induction generator based wind power generation system is proposed based on the fractional frequency power transmission. A control method aimed at increasing efficiency and maximizing energy capture using the field orientation control（FOC） technology is introduced， considering the wake effects. Two types of wind power generation system i.e. VSVF and constant-speed constant-frequency（CSCF） system are modeled and analyzed. Simulation results with PSCAD/EMTDC demonstrate that the optimal power efficiency tracking and optimal wind power capturing can be achieved.