Enhanced stability delay margins of load frequency control systems using pitch-angle-based deloading operation of variable-speed wind turbines

Abstract

This study investigates the enhancement of stability delay margins (SDMs) in load frequency control (LFC) systems supported by the pitch angle control-based deloading operation of wind turbines (WTs). The integration of WTs through power electronic converters reduces system inertia. To address this stability issue, virtual inertia control (VIC) enables WTs to temporarily release stored rotor kinetic energy, modulating active power in response to frequency deviations and the rate of change of frequency. In addition, the deloaded WTs provide a power reserve that supports primary frequency control. However, the extensive use of communication networks in LFC introduces network-induced delays that can degrade system stability. In this regard, the direct method is applied to the LFC—WT system to determine exact SDMs for constant communication delays. Quantitative analysis shows that the inclusion of deloaded WTs increases the SDMs by more than 200% across a practical range of control parameters. The theoretical results are validated using MATLAB/Simulink and the Quasi-Polynomial Mapping-Based Root Finder (QPmR) algorithm, which verifies the theoretical critical roots by detecting dominant roots in the complex plane. The SDM analysis shows that WT deloading combined with inertia support substantially improves delay tolerance and enhances frequency support performance in the LFC system.