Scope

The widespread utilization of distributed generation highlights the appeal and feasibility of microgrids (MG). Decentralizing the electrical grid into smaller, self-sufficient segments enhances system resilience and operational continuity during disruptions, particularly under extreme conditions such as natural disasters or armed conflicts. Through the implementation of microgrid architectures that facilitate localized generation and consumption, critical power supply can be sustained even when the grid infrastructure is compromised. These MGs with high share of inverter-based generation rely heavily on grid-forming (GFM) inverters to provide voltage and frequency reference for the conventional grid-following (GFL) inverters.

To enable islanded operation, MG necessitates the capability of autonomous resynchronization to the main grid. GFMs are ideal assets for this, as they directly control the voltage and frequency of the local grid.

Methods

In our work we seek to investigate the capabilities of GFM inverters to successfully resynchronize the local grid considering (1) line impedances between inverters and the point of common coupling of the MG, (2) the share of GFM power relative to the overall power capacity of the MG and (3) the operating points of each individual GFM inverters. Through simulations, we also evaluate and enhance the tuning of the dedicated control scheme that facilitates reliable resynchronization among multiple GFMs.

The topic was investigated both in Matlab Simulink simulation and in laboratory environment through Power Hardware-in-the-loop (PHIL) simulations. The laboratory setup contained multiple physical assets as well as an extensive low voltage distribution system with multiple consumers and prosumers implemented on a real-time simulator.

Main results

We present a thorough investigation of multiple GFM inverters’ ability to cooperate in reconnecting a local grid based on multiple aspects. Key factors include the positioning of the GFM in relation to local consumers and prosumers, as well as the microgrid’s point of interconnection with the main grid, along with the nominal power and operational setpoints of the GFMs relative to local energy demand and generation capacity.