Stability Control for Wind in Weak Grids

4 Hz oscillations and 30 Hz oscillations have been observed in real-world wind farms with weak grid interconnections. Such stability issues limit wind power delivery. This paper proposes mechanism-based feedback control strategies suitable for vector control based voltage source converters employed in Type-3 and Type-4 wind to enhance the overall system stability. Using a simplified linear model, we first demonstrate that the root cause of weak grid stability issue is due to the coupling of power delivery and voltage at the point of common coupling (PCC). Increasing power delivery leads to a reduction in the PCC voltage. This relationship establishes a mechanism that may lead to instability in weak grid scenarios. The proposed control strategies reduce the coupling between power and voltage. Two feedback control strategies are introduced to modulate the power order or dc-link voltage order with either the d-axis current or the PCC voltage as the input signal. The control strategies are tested on analytical models and MATLAB/SimPowerSystems testbeds of Type-3 wind and Type-4 wind. The PCC voltage feedback control demonstrates excellent capability of stability enhancement. With the proposed control, power delivery of wind can be significantly improved.