D-Q Small-Signal Impedance Modeling of Load Virtual Synchronous Machine and Stability Analysis in Weak Grid

With power electronic loads penetrating into grid increasingly, the power grid is progressively developing into low inertia and less damping network, which seriously leads to the instability problems. To address the issues, the load virtual synchronous machine (LVSM) technology is introduced for the ability to support inertia and damping. And the control scheme is described in details, with not only power loops but inner ac voltage and current loops. Then taking the dc-side voltage into account, the d-q small-signal output impedance model of LVSM is derived, and the impedance of the LVSM behaves inductive, being consistent with the grid impedance characteristics in the middle and high frequency areas. Based on GNC, the stability between the LVSM and the weak grid is analyzed for the first time. And the stability analysis result shows that LVSM remains stable in weak grid. Finally, the simulation results are shown to verify the d-q impedance model and the stability analysis.