Steady-state Solution and Evaluation Indices of DFIG Operating at Synchronous Speed (sDFIG)

Abstract

The doubly-fed induction generator (DFIG) reduces the inertia and frequency regulation capability of power systems. With the supplementary control, they may operate as the virtual synchronous generator to respond to frequency change. A DFIG may yield the inertia by operating at synchronous mode (sDFIG). The critical wind speed with the optimal rotor speed equal to the synchronous speed is found to decide the suitable sDFIG. Steady-state solution to the sDFIG orientated by the rotor flux and the stator voltage is proposed. The energy conversion efficiency and reactive power capability are proposed for the sDFIG. It is found that the DFIG with wind speed less than the critical wind speed is suitable as sDFIG. The efficiency of the sDFIG with lower wind speed is less, but the reduction of active power is less than that with higher wind speed. With lower wind speed, reactive power capability of the sDFIG is wider than the DFIG.