Internal Modal Resonance Analysis for Full Converter-based Wind Generation using Analytical Inertia Model

Full converter-based wind generation (FCWG) has become a prevailing choice in new wind farms. It is usually regarded that low short circuit ratio (SCR) or weak grid is a key condition to induce oscillations associated with wind farms. However, we have recently discovered a rare phenomenon that even in a strong grid with a large SCR, the internal modal resonance of FCWG can still lead to oscillations and threaten the converter-driven stability. To determine the internal modal resonance in FCWG, a novel analytical inertia model (AIM) is derived to elaborate all oscillation modes of FCWG (FOMs) for the first time. The derived model reviews the complex relations of all FOMs in a formulaic manner, which not only provides guidance on parameter resetting, but also illuminates how FOMs interact with each other. On this basis, an equivalent transfer function is integrated into the state space equation to characterize the interaction effect, and a universal torque model is proposed to yield insights into the mechanism of internal modal resonance owing to the variation of operating conditions. Furthermore, the effectiveness of AIM is substantiated as well as the analysis method, and the unusual event of internal modal resonance is also demonstrated.