Single stationary domain equivalent inverter admittance for three-phase grid-inverter system considering the interaction between grid and inverter

Admittance matrix has been used to represent the characteristics of three-phase inverter for grid-inverter system stability evaluation in both stationary, sequence, and dq domain. For the dq domain admittance matrix, the PLL and Park transformation introduce additional dynamics during the admittance measurement that may influence the application of dq model. For the stationary and sequence domain admittance matrix, the model measurement is not affected by the above additional parts but may also encounter other difficulties in actual measurement. First, current frequency response analyser (FRA) is not able to perform two-frequency measurement required by the admittance matrix. Second, practical limitations exist in the course of solving complex-valued admittance matrix equations. Here, a single stationary domain equivalent admittance of three-phase inverter for grid-inverter system with considering the interaction between grid and inverter is defined so that the above two difficulties can be avoided. Then, an equivalent admittance model of prototype inverter is constructed for stability analysis of the grid-inverter system using Nyquist stability criterion, instead of the generalised Nyquist criterion (GNC). The effectiveness of the proposed equivalent inverter admittance model is validated through simulation and experiment verification.