Frequency Support From a Fixed-Pitch Type-2 Wind Turbine in a Diesel Hybrid Mini-Grid

Frequency stability is an important issue in small diesel hybrid autonomous power systems (mini-grids) with high penetration of wind power. With large variations of wind power and load demand, the rate of change of frequency (ROCOF) and frequency excursions tend to increase what can lead to load shedding and tripping of renewable energy generators. The power required from the grid-forming diesel engine generator sets (gen-sets) to balance the system tends to vary more, resulting in increased unit cycling. These problems can be mitigated with costly energy storage units and sophisticated wind turbines (WTs) that provide frequency support via active power control. This paper presents an approach for introducing a power (P) versus frequency (f) droop characteristic in a low-cost fixed-pitch wound rotor induction generator (WRIG)-based WT that allows it to provide frequency support. The effectiveness of the proposed technique in reducing frequency and power demand variations from the diesel power plant is demonstrated by means of simulations.