Stand-Alone Doubly-Fed Induction Generators (DFIGs) With Autonomous Frequency Control

This paper presents an innovative control which enables a wind farm based on doubly-fed induction generators (DFIGs) to continue operating on islanding because: 1) each stand-alone DFIG has autonomous frequency control over its stator voltage; 2) multiple units of such DFIGs synchronize to form a common wind farm grid frequency; and 3) the DFIGs share the wind farm load by using the common wind farm frequency to implement frequency droop control. Autonomous frequency control is based on integrating the properties of phase-locked loops (PLL) with decoupled P - Q control to produce self-sustaining stator voltages by feedback.