Reduced-Order Analytical Models of Grid-Connected Solar Photovoltaic Systems for Low-Frequency Oscillation Analysis

Low-frequency oscillations have been observed in a real-world solar photovoltaic (PV) farm. The goal of this research is to build a simplified analytical model in the synchronous frame for large-signal simulation and small-signal analysis. The latter, e.g., eigenvalue analysis and participation factor analysis, can reveal influencing factors of the oscillations. Two simplified analytical models are proposed, ignoring PV dc-side dynamics (e.g., dc/dc boost converter control and maximum power point tracking), while preserving the grid-side converter (GSC) controls and electromagnetic dynamics of the grid interconnection. The first model assumes the input power from PV's dc side known and constant. The second model assumes that PV's dc side is represented by a constant dc voltage behind an impedance. The simplified models are compared with an electromagnetic transient (EMT) testbed with full details on time-domain simulation results, admittance frequency-domain responses, and eigenvalue-based stability analysis results. The second simplified model is found as capable of accurately predicting oscillation stability.