Analysis of LFOs and Resonance in VSG-Controlled PMSG-Based Wind-Driven System

The grid-forming inverter, with excellent adaptability to weak power grids, is positioned to be the foundation of future high-proportion power grids. Moreover, virtual synchronous generator (VSG) control is recognized as the mainstream control strategy for grid-forming inverters. For permanent magnet synchronous generator (PMSG)-based wind-driven systems, connecting to the power grid via VSG-controlled inverters introduces novel impacts on the system's low-frequency oscillations (LFOs) in power grids. Impact One involves the negative/positive damping effect on LFOs. In this paper, the small-signal torque model of VSG-controlled PMSG-based wind-driven system is established based on damping torque method, revealing the mechanism of machine-side dynamics on LFOs and proving the necessity of double-mass model for accurate stability analysis Impact Two is the resonance effect between torsional oscillation and LFOs. Subsequently, the paper uses open-loop resonance analysis method to study this resonance mechanism and to predict the root trajectory. Finally, the analysis's effectiveness is validated through a case study involving the connection of a VSG-controlled PMSG-based wind-driven systems to a four-machine two-area system.