Frequency Stability Support of a DFIG to Improve the Settling Frequency

To ensure the frequency stability of a power grid, the settling frequency following a frequency event should be stabilized within the maximum steady-state frequency deviation (SSFD) band. If the frequency is stabilized at a value beyond the maximum SSFD band for high penetrations of variable renewable energy, the frequency cannot be restored to the nominal frequency because automatic generation cannot be activated. This paper proposes a primary frequency control support scheme of a doubly-fed induction generator (DFIG) to improve the settling frequency following an event. In the proposed scheme, if the frequency following an event is stabilized at a value beyond the maximum SSFD band, to reduce the output power of synchronous generators, the output power of a DFIG is instantly increased by a constant and maintained until the frequency increases to within the maximum SSFD band. At the same time, the mechanical input power of the synchronous generators is maintained so that the difference between the mechanical input power and electrical output power of the synchronous generators increases the frequency to a value within the maximum SSFD band. The simulation results demonstrate that the proposed scheme can improve the settling frequency while avoiding additional system defense plans when the settling frequency is stabilized at a value beyond the maximum SSFD band.