Limiting Transients for Grid-Forming Inverters Using a Phase Limiter

This paper details in a comprehensive manner the connection and disconnection of grid-forming inverters with proposed protection measures to avoid spikes and high currents in transients. For smoothing the transients, the paper proposes a new protection scheme based on imposing a limitation on the difference between the grid and inverter phase angles to avoid rush currents in addition an automatic circuit breaker for utility grid connection. The paper presents the inverter’s main control loops in which the proposed protections are added. The proposed protections are validated in an experimental setup of two grid-forming three-phase inverters with a connection to the utility grid. It clearly shows the transients of the inverter’s connection and disconnection processes in three different conditions: 1) standalone operation of an inverter, 2) connection of the inverter to an existing micro grid, 3) the connection and disconnection of the external utility grid while the inverter is connected to the micro grid.