Modelling and Analysis of Frequency-Responsive Wind Turbine Involved in Power System Ultra-Low Frequency Oscillation

This paper presents a dynamic analysis for ultra-low frequency oscillations (ultra-LFOs) observed in the wind-hydropower hybrid systems. In such systems, DFIG wind turbines (WTs) are required to be frequency-responsive with providing the inertia and frequency support. First, this paper establishes an analytical model to capture the dynamics of frequency-responsive DFIG WTs at the electromechanical timescale. A systematic analysis is then conducted on a 2-machine system (include a hydraulic generator (HG) and an aggregated DFIG WT) to reveal WTs' dynamic behaviors and their interference mechanism with the HG, accounting for the system ultra-LFO mode. The result shows that WTs' frequency control, speed control, MPPT control and pitch control would be involved in the system ultra-LFOs, but they have different effects under different operating modes. Cases studies are carried out on the 2-machine system and a modified 10 machine 39-bus New-England power system. Based on the modelling effort and simulation studies, some recommendations are made for using DFIG WTs to help damp the ultra-LFO in wind-hydropower hybrid systems.