Control of a DFIG Based Wind Turbine as a VSG (DFIG‐VSG)

Abstract

This chapter presents a control strategy to operate a doubly‐fed induction generator (DFIG) based wind turbine as a virtual synchronous generator (VSG), after revealing the analogy between differential gears and DFIGs. An electromechanical model is presented to represent a DFIG as a differential gear that links a rotor shaft driven by a prime mover (wind turbine), a virtual stator shaft coupled with a VSG and a virtual slip shaft coupled with a virtual synchronous motor. The chapter also presents the concept of a DFIG‐VSG to operate the whole DFIG‐converter system as one VSG with the stator shaft synchronously rotating at the grid frequency, even when the rotor shaft speed changes, through controlling the virtual slip shaft to synchronously rotate at the slip frequency. A prominent feature is that there is no need to adopt a phase‐locked loop, either on the grid side or on the rotor side. Simulation and experimental results are also presented.