Effects of Droop Based Fast Frequency Response on Rotor Angle Stability During System Wide Active Power Deficits

The effects of fast frequency response (FFR) on rotor angle stability have predominately been established by examining the oscillatory behavior of synchronous generators (SGs). What remains largely unexamined, however, is the effect that FFR has on the angle separation and power transfer between SGs. This paper systematically examines the evolution of the angle separation and power transfer between SGs during FFR provision in the context of frequency containment events. Droop based FFR schemes, which are popular and effective in practical systems, are analyzed. This research investigates how the location of the initiating system wide active power deficit, the location of resources providing FFR, and the delays associated with FFR provision all impact rotor angle stability. The key results are obtained using a modified IEEE 39-bus system and further verified using a reduced-order dynamic Great Britain system model. The results show that the angle separation and power transfer between SGs decrease when power deficits occur in areas with extensive generation sources which, conversely, implies that angle stability deteriorates if power deficits occur near load centers. A key finding is that providing the FFR at locations closest to the source of the initial power deficit does not always enhance angle stability, and sometimes has a significant adverse effect. The effect that FFR delays have on rotor angle stability is explained, highlighting the necessity to carefully consider and design FFR provision timing, particularly in areas with diminishing levels of inertia.