Coordinated Frequency and Voltage Regulation of Grid-Following and Grid-Forming Inverters

In a purely inverter-based microgrid, both grid-forming (GFM) and grid-following (GFL) inverters will have a crucial role to play in frequency/voltage regulation and maintaining power sharing through their grid support capabilities. Consequently, the coordination between these two technologies becomes increasingly important for optimal system performance. However, the existing work does not consider GFL's potential to participate in a secondary control in coordination with GFM, thus not able to utilize the full capability of inverter resources. In this paper, we show that it is possible to fully coordinate the GFL and GFM inverters to achieve accurate power sharing, frequency/voltage regulation, and circulating var mitigation in networked microgrids even without the support of any synchronous generators or the bulk power system. We use the leader-follower consensus framework to develop a GFM-GFL coordination control. The effectiveness of the proposed coordination is verified under different disturbances and communication degradation. In addition, we find that the proposed fully-coordinated secondary control outperforms other approaches such as un-coordinated and partially-coordinated secondary controls, in aspects of load sharing and frequency and voltage regulation. Overall, this study emphasizes the need and benefits of GFL-GFM coordination in microgrids.