Consensus Control for Coordinating Grid-Forming and Grid-Following Inverters in Microgrids

In a 100% 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 utilizing the full capability of inverter resources. In this paper, we present an automatic secondary control scheme that fully coordinates the GFL and GFM inverters to achieve frequency/voltage restoration, accurate power sharing, 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 the GFM-GFL coordinated secondary control, in the absence of a centralized controller. The proposed coordination is effective under different disturbances, and can work in a plug-and-play manner. 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.