Hybrid system consisting of synchronous condenser and virtual synchronous generator for enhanced power quality in microgrid

Virtual synchronous generator (VSG) has been widely researched and applied to converters for their grid-forming capabilities. However, the intrinsic coupling between the active and reactive power outputs of VSGs negatively impacts the power quality delivered to the grid, particularly in microgrids. When VSG is compensating for the reactive power imbalances, the active power output will concurrently change, leading to a variation of frequency. Although existing literature proposes various improvements to decouple these power outputs, complete decoupling cannot be achieved solely by VSGs. This letter analyses the coupling mechanism and investigates a hybrid approach combining a VSG and a synchronous condenser (SC) to mitigate this effect, improving the power quality. Additionally, this study modifies the traditional reactive power control of VSGs to ensure voltage stability during transients. Test cases are carried out to verify the effectiveness of the proposed method. The results show that the system active and reactive power are effectively decoupled, and it maintains the frequency while regulating the grid voltage.