<p>Conventional pre-synchronization methods for virtual synchronous generators (VSGs) during the transition from islanded to grid-connected mode typically rely on a phase-locked loop (PLL), resulting in complex structures and slow dynamic responses. Existing non-PLL approaches often involve tedious parameter design and high computational complexity. To address these issues, a direct voltage pre-synchronization control strategy based on voltage vector geometry is proposed in this paper. The proposed method employs the orthogonal relationship between the VSG output voltage vector and the grid voltage vector as the synchronization criterion. By computing the dot product of these two vectors, the phase control signal is obtained, enabling accurate phase tracking with only a single PI regulator, eliminating the need for PLLs and complex coordinate transformations. Simulation and experimental results demonstrate that the proposed strategy achieves rapid synchronization of voltage amplitude and phase within 2–3 power cycles. During islanded to grid-connected transitions, the grid-connected current remains smooth and surge-free with undistorted voltage waveforms. For grid-connected to islanded transitions, the inherent voltage source characteristic of the VSG enable a seamless transition, enhancing the dynamic performance and reliability of VSG mode switching.</p>