Unified Synchronization Control of Grid-Forming Voltage-Source Converter for Maximum Inertia Power Support With Enhanced Synchronization and DC-Link Voltage Stability

Grid-forming (GFM) voltage-source converters (VSCs) are expected to provide inertia power support during grid-frequency disturbances and grid-voltage phase-angle jumps. However, the existing synchronization control methods have unsatisfactory performance to control the GFM VSCs to provide the maximum inertia power support while achieving robust synchronization and DC-link voltage control during these transient events. To bridge this gap, this paper proposes a novel unified synchronization control (USC) strategy that integrates an active power compensator with a DC-link voltage compensator through a parallel configuration. With the proposed USC, the GFM VSC can autonomously and seamlessly switch its operation between two modes: a voltage-controlled DC-side source (VC-DCS) mode when the DCS current is within the limit and a current-controlled DCS (CC-DCS) mode when the DCS current reaches the limit, while providing the maximum inertia power support. Compared to the state-of-the-art power synchronization control (PSC) and DC-link voltage synchronization control (DVSC) methods, the USC significantly enhances the transient oscillation damping as well as synchronization and DC-link voltage stability. A parameter design methodology for the USC is presented. Finally, the superiority of the proposed USC over the PSC and DVSC is validated by a loop-gain evaluation using simulation as well as grid-frequency step change and grid-voltage phase-angle jump tests using a GFM VSC hardware testbed.