Stability Analysis of a Grid-Forming Inverter by Complex Vector Control in αβ Domain

Abstract

This paper proposes a stability analysis method for a grid-forming inverter with a droop-control in the sequence domain. The analysis is based on the impedance method. First a system operating point is determined and linearized around the point to calculate output impedance of the inverter. Then output responses of the inverter are analyzed for an excitation small-signal in the frequency domain. The feedback control is processed only in the sequence domain. However, the complex conjugate operation in the droop control is found to transform variables equivalently into the synchronous domain. The frequency analysis is processed in a sequence/synchronous mixed domain. Operation behaviors and critical conditions are investigated and validated analytically and experimentally.