Harmonic Stability and Resonance Analysis in Large PMSG-Based Wind Power Plants

Compared to the conventional power systems, large Wind Power Plants (WPPs) present a more challenging system where the interactions between the passive elements and the wideband control systems of power converters may result in harmonic instability and new resonance frequencies. Most of researches about harmonic stability focus on small-scale systems, and it has not pay much attention yet to identify the mentioned resonance frequencies. This paper models and analyzes the harmonic instability and resonance frequencies in large Permanent Magnet Synchronous Generator (PMSG) based WPPs with full-scale converters, where linearized models of inner control loops of the power converters are considered. A large PMSG-based WPP introduces as a Multi-Input Mulit-Output (MIMO) control system, therefore, the stability of the whole power system is analyzed based on the real parts of the poles of the introduced MIMO system and the resonance frequencies are identified based on the element amplitudes of the MIMO matrix. An active damping controller is used to set the poles of the WPP in a desired location in order to mitigate the harmonic instability problems. Multiple case studies are provided to depict that Wind Turbine (WT) connections or disconnections in a WPP, as well as grid impedance variations can effect the harmonic stability and resonance frequencies. The effectiveness of the presented theoretical analysis is validated by time-domain simulations of a 400-MW WPP in PSCAD/EMTDC software environment.