Stability Comparison and Analysis of the VSG Controlled under Different Coordinate Systems

It has been revealed that the virtual synchronous generator (VSG) shows good stability performance in weak grid and may suffer from oscillations in strong grid. When connected to the three-phase power grid system, grid-connected voltages and currents of the VSG are usually controlled under dq coordinate system or $\alpha \beta$ coordinate system, which coordinate system is better for the VSG to avoid oscillations in strong grid is still unclear. To address that issue, this paper carries out the stability comparison and analysis of the VSG controlled under dq and $\alpha \beta$ coordinate system, respectively. Sequence-impedance models are built and validated for the VSG controlled under different coordinate systems, based on which stability comparison are carried out and key control parameters that influence the stability are figured out. It is revealed that the VSG controlled under dq coordinate system shows better stability in strong grid than the VSG controlled under $\alpha \boldsymbol{\beta}$ coordinate system. Additionally, the voltage and current control parameters have different influences on low-frequency stability of the VSG controlled under different coordinate systems in strong grid. The theoretical conclusions are also verified via simulations.