Inertia-Free Stand-Alone Microgrid - Part I: Analysis on Synchronized GPS Time-Based Control and Operation

The inertia-free stand-alone (IFSA) microgrid is the new small power grid without synchronous generators equipped in conventional power systems. In other words, this system has the only converter-based generators (CBGs) based on energy storage devices and renewable energies. Therefore, it requires a new CBG control to provide strong voltage reference for the CBGs connected to the point of common coupling (PCC). This is because the IFSA microgrid is subject to a weak system such that it cannot maintain its rated frequency and/or bus voltage with the conventional real and reactive power controllers, which usually get their references from the PCC. This paper proposes the innovative conceptual approach for distributed coordination in the IFSA microgrid by applying the synchronized global positioning system time to the CBGs. Moreover, it is verified that the proposed physical structure of the IFSA microgrid makes it possible for all CBGs to share the real and reactive powers effectively. As the result, the proposed CBG control can provide the robustness, which is strongly required in the IFSA microgrid, based on timely outage management and restoration process. Several case studies are carried out with the microgrid of 36 MW to verify the effectiveness of the proposed CBG controller. The simulation and hardware-in-the loop tests are carried out using the power system computer-aided design/electromagnetic transient design and control (PSCAD/EMTDC) and the real-time digital power system simulator (RTDS), respectively.