Synchronous Frequency Resonance Of Virtual Synchronous Generators And Damping Control

The penetration of renewable energy sources (RES) is increasing due to the global energy crisis and environmental pollution issues, such as wind and solar energy. The voltage source converters (VSCs) are the main components for interfacing RES into the utility grid. The control strategy that VSCs emulate the behaviors of synchronous machines is an effective solution for high-penetration RES integrating into the power system. However, the inherent resonance at synchronous frequency exists with this control strategy, which deteriorates the power system stability. This paper explores the physical reasons and exact characteristics of synchronous frequency resonance (SFR).1. The rigorous VSG phasor model is derived over the whole frequency range, which indicates that SFR is caused by the flux dynamics. Based on the phasor model, the small-signal models of VSGs are established, including model of active power versus phase angle and that of reactive power versus voltage magnitude. It reveals that the SFR has a negative impact on VSG stability, which may be excited with inappropriate controller parameters, thereby inducing the power oscillations. These dynamics are often neglected in a real SG because of the slow mechanical reaction, but may be excited in a VSG due to the fast regulation ability of power electronic converters.2. Moreover, the dynamic coupling effect between the active power and reactive power controllers is disclosed, which accentuates the resonance phenomena and reduces the stability margin.3. In order to suppress the resonance at synchronous frequency, two active damping control methods are proposed, which suppress the SFR through optimizing the control parameters or adding virtual electrical resistance. Finally, the effectiveness of the theoretical conclusions is verified experimentally.