Assessment of Voltage Support Capability for Virtual Synchronous Generators

When droop control of virtual synchronous generators (VSGs) with rotational inertia is adopted in islanded alternating current (AC) microgrids, the coupling mechanism among reactive power loads, control parameters and system virtual inertia remains unclear, and there is a lack of quantitative evaluation schemes. To address this issue, this paper proposes a quantitative evaluation method for virtual inertia based on a reduced-order equivalent model. First, the control system of grid-forming converters is simplified to construct a reduced-order model for microgrid voltage support, and the analytical expression of voltage dynamics and the calculation formula of the system-level inertia time constant are derived. Subsequently, a three-dimensional response surface is utilized to multi-dimensionally analyze the influence laws of filter cutoff frequency, reactive power load, rotational inertia and damping coefficient on system inertia and steady-state voltage drop. Finally, a reduced-order model of the AC microgrid is established based on the RT-Lab hardware-in-the-loop (HIL) experimental platform, and multiple sets of results validate the correctness of the theoretical analysis.