Stability Analysis and Improvement of Three-Phase Grid-Tied Power Converters through the Generalized Phase Portraits Method

Three-phase grid-tied power converters may exhibit strong nonlinearity and complex behaviors in the face of severe voltage sags and grid faults, where small-signal models are invalid. As such, this paper proposes a novel large-signal model—a modified state-space average model—of three-phase grid-tied power converters. Through the generalized phase portraits analysis, the proposed model accurately predicts stability problems and identifies stable regions as well as decisive design parameters. More importantly, this paper proposes a novel saturation controller based on space division, and the effect of stability improvement is further analyzed. Finally, simulation and experimental results clearly validate the effectiveness of the proposed model, stability analysis, and controller.