Comparison of the Response of Doubly Fed and Fixed-Speed Induction Generator Wind Turbines to Changes in Network Frequency

TLDR

Synchronous and fixed‑speed induction generators release kinetic energy when system frequency falls, while DFIG‑based turbines use a rotor‑speed‑dependent control to restrain torque. The authors aim to show that the DFIG control, which is independent of system frequency, contributes little to system inertia. They modified the DFIG control to incorporate an inertia‑response component. Simulations indicate that with this modification, the DFIG turbine can supply substantially more kinetic energy than a fixed‑speed turbine.

Abstract

Synchronous and fixed-speed induction generators release the kinetic energy of their rotating mass when the power system frequency is reduced. In the case of doubly fed induction generator (DFIG)-based wind turbines, their control system operates to apply a restraining torque to the rotor according to a predetermined curve with respect to the rotor speed. This control system is not based on the power system frequency and there is negligible contribution to the inertia of the power system. A DFIG control system was modified to introduce inertia response to the DFIG wind turbine. Simulations were used to show that with the proposed control system, the DFIG wind turbine can supply considerably greater kinetic energy than a fixed-speed wind turbine.