The paper covers the steady-state analysis of a wound-rotor induction generator operated at varying shaft speeds in the subsynchronous and supersynchronous regions, by control of both the magnitude and direction of slip power. A modified equivalent circuit is used in the analyses in which core losses and harmonics are ignored. The resulting nonlinear algebraic equations are solved numerically. An optimum control strategy, which maximises the total electrical power output of the double output induction generator is determined, and theoretical results are verified experimentally with particular emphasis on the system including naturally commutated convertors. The limitations of naturally commutated convertor circuits and their effects on the output power characteristic of the system are also discussed. This system shows considerable advantage in the field of wind-energy conversion. Its performance is optimised on the basis of annual energy production by calculating optimum values of gear ratio and generator size for the given turbine characteristic and site wind regime. Also, a comparison is made among optimised versions of alternative induction generator schemes used in wind-energy conversion systems, on the bases of annual energy production and transfer characteristic for the same site and turbine.