SSR Stable Wind Speed Range Quantification for DFIG-Based Wind Power Conversion System Considering Frequency Coupling

The subsynchronous resonance (SSR) characteristics of doubly-fed induction generation-based wind power conversion system (DFIG-WPCS) varies with the wind speed. Obtaining the small signal SSR stable wind speed range is urgently important for wind farm dispatch planning. However, there are few methods to quantify the small signal SSR stable wind speed range of DFIG-WPCS. Moreover, the inherent frequency coupling when DFIG-WPCS is integrated to modular multilevel converter-high voltage direct current (MMC-HVDC) may lead to inaccurate stability assessment results. In this article, the frequency coupling mechanism between WPCS and MMC is revealed by analyzing the law of harmonic interaction in the interconnected system. The wind speed-frequency two-variable equivalent admittance model of DFIG-WPCS is established by taking the frequency coupling account. Relying on the two-variable open-loop transfer function, the multiple phase margin contours plot approach is proposed to quantify the small signal SSR stable wind speed range and damping properties. The effectiveness of two-variable admittance and analysis method are validated against electromagnetic transient (EMT) testbed with MATLAB /SimPowerSystems. The analysis results can provide a reference for the early planning and stable operation of DFIG-WPCS.