Peak Shaving Control for a Virtual Synchronous Generator in Island Grids

A virtual synchronous generator (VSG) can be considered a voltage source with an emulated inertial response. Depending on the grid condition, however, it is necessary to limit the output current, which renders the inverter dynamics and makes the inverter prone to losing synchronism with the grid. To address this well-known challenge, in this article, we propose a novel control method for a VSG that can achieve current limiting with stability. We describe the proposed VSG with block diagrams and validate its control responses with transfer functions. The proposed VSG can be useful to enhance the frequency stability of an island grid, which is more vulnerable to disturbances by nature than a large interconnected system. We use a hardware-in-the-loop (HIL) setup for further validation. Using the HIL environment, we test the proposed VSG in an island system operating with diesel generators for generator trips, low-frequency oscillations, and voltage sags. We also test the VSG in a single-inverter-infinite-bus setup to evaluate its transient stability and compare it to ones with conventional current-limiting methods. Although the current limiting shaves the peak power of the VSG, it ensures continuous inertial and damping responses without compromising stability.