Nonlinear Stability Boundary Assessment Of Wind Power Plants Based on Reverse-Time Trajectory

Abstract: This letter determines the nonlinear stability boundary of a wind power plant (WPP) connected to an AC power grid via a long HVAC cable. The analysis focuses on the slow Phase-Locked Loop (PLL) dynamics, with an assumption that the fast current control dynamics can be neglected. To begin, we propose an aggregated reduced-order wind turbine model. This aggregation can be applied up to a limited frequency, e.g. 400Hz, which aligns with our assumption regarding low-frequency dynamics. The WPP collector and transmission network model is established using impedance/frequency scan approximated around $\pm$5 Hz of the PLL nominal frequency, accounting for the hard saturation limits. The stability boundary of the reduced-order system is determined by reverse time trajectory, offering valuable insights into the WPP's overall stability. The work presents a routine from modelling to nonlinear stability assessment for offshore wind farm applications.