With the widespread integration of renewable energy devices, power grids are weakening, system inertia levels continue to decline, and system frequency faces severe instability risks. Traditional static var generators (SVGs) adopt grid-following control, which leads to performance degradation in weak grids and fails to provide inertial support. To address this issue, this study proposes a grid-forming SVG control strategy and internal energy management scheme based on a modular multilevel converter (MMC) topology by emulating a virtual synchronous generator (VSG). First, the topology and operating principles of the MMC were analyzed. Second, an outer-loop energy control scheme for the grid-forming SVG was designed using DC-side capacitor dynamic equations. A small-signal model of the grid-forming SVG was established to analyze the impact of inertia and damping on system stability. Subseuqently, the internal energy transfer process within the MMC was analyzed, and an internal energy balancing control scheme was proposed. Finally, MATLAB-based simulations verify the effectiveness of the proposed control strategy.
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