Analysis of Stator-controlled Doubly-fed Induction Wind Generator for Fractional Frequency Transmission System

In this paper, a stator-controlled doubly-fed induction wind generator (SC-DFIG) designed for fractional frequency transmission system (FFTS) is presented. To accommodate the low-frequency voltage of the FFTS, the SCDFIG connects the rotor winding directly to the grid, while the stator winding is linked through a back-to-back AC/AC converter. The system topology and unique operating principles of this innovative winding and control scheme are thoroughly analyzed, along with the mathematical model of the SC-DFIG. Based on theoretical analysis, the effectiveness and feasibility of the stator-controlled scheme are verified through multi-condition simulations and prototype experiments. Contrary to traditional rotor-controlled doubly-fed induction generator (RC-DFIG), this novel stator-controlled fractional frequency generator features a constant-frequency rotor and a variable-frequency stator. The proposed system maintains high-speed operation even at low frequencies, delivers excellent electromagnetic performance, and achieves low per-unit power cost for whole generator system.