Abstract: To realize variable-speed-constant-frequency (VSCF) output power of wind energy conversion system (WECS) and to lower the cost of frequency-conversion system, a novel approach of flexible hybrid-driven unit for wind energy conversion system is presented. The realizing theory of this approach and the fundamental structure of the hybrid-driving differential transmission are described. Three axes rotor speed relationship is analyzed from kinematical point of view. The calculation formula of the key parameters of the controllable servomotor as timing amplifier, timing depth, and timing bandwidth are given. With sample parameter data, the charac-teristic parameters of this VSCF transmission of WECS under the rated speed are calculated. The results show that, with the steady output of wind power, this system can realize maximum power point tracking (MPPT).

Key words: Planetary gears, Power splitting, Variable-speed-constant-frequency, Wind energy conversion system