Small-Signal Stability Analysis of Voltage Source Inverters Operating under Low Short-Circuit Ratios

Stability issues typically arise when inverter-based renewable energy generation connects to busbars in the power grid containing a low short-circuit ratio. This paper presents a small-signal model of a grid-feeding inverter incorporating dynamics associated with the current regulator, pulse width modulator, phase-locked loop, and interconnecting filter. We apply the fast voltage stability index (FVSI) to characterize the system’s dynamic operating limits for a wide range of inverter operating points. The grid’s physical limitations are shown to be more pronounced when the inverter operates at a leading power factor. Furthermore, eigenvalue trajectories highlight the criticality of appropriately selected current regulator gains. Last, participation factor analysis illustrates changes in the system’s states’ behavior as the short-circuit ratio decreases.