Grid-forming converters are attracting attention for their significant advantages in terms of stability in a weak grid and simulated inertia. However, while they offer great flexibility due to the use of power semiconductors, they are also affected by their low current-carrying capacity. This means that during a fault, instead of the usual voltage control, a current limiting control is active, which changes the dynamic performance of the converter and influences transient stability. This manuscript focuses on the dynamic performance of grid-forming converters during the restart phase at the post-fault period, and proposes an initial phase threshold to prevent the converter from going into current saturation. Based on this, the manuscript proposes several restart strategies during the post-fault period, by using some fast resynchronization methods in order to meet the requirements of the converter’s stable operation and fast active power restoration. Finally, the above findings and the proposed strategies are validated by a joint control hardware-in-the-loop system.

The central components influencing future grid stability in the future are inverters and their controllers. This paper delves into the pivotal role of inverters and their controllers in shaping the future stability of grids. Focusing on grid-supporting inverters, the study utilizes a microgrid test setup to explore their impact on overall grid stability. Employing impedance-based stability analysis with the Nyquist criterion, the paper introduces variations in internal inverter parameters and external grid parameters using pole-zero map considerations. The inverter’s control structure, resembling standard generators with droop control, facilitates the application of grid operators’ knowledge to inverter control. Mathematical insights into stability principles are provided, highlighting the influence of poles related to the phase-locked loop and the strategic placement of additional poles for enhanced stability. Furthermore, the paper evaluates the effects of rotating inertia, revealing that a 50% increase in system inertia can stabilize unstable microgrid behavior, enabling grid-supporting inverters to actively contribute to grid reliability.

The deployment of PV inverters is rapidly expanding across Europe, where these devices must increasingly comply with stringent grid requirements. This study presents a benchmark analysis of four PV inverter manufacturers, focusing on their Fault Ride-Through capabilities under varying grid strengths, voltage dips, and fault durations—parameters critical for grid operators during fault conditions. The findings highlight the influence of different inverter controls on key metrics such as total harmonic distortion of current and voltage signals, as well as system stability following grid faults. Additionally, the study evaluates transient stability using two distinct testing approaches. The first approach employs the current standard method: testing with an ideal voltage source. The second utilizes a Power Hardware-in-the-Loop methodology with a benchmark CIGRE grid model. The results reveal that while testing with an ideal voltage source is cost-effective and convenient in the short term, it lacks the ability to capture the dynamic interactions and feedback loops of physical grid components. This limitation can obscure critical real-world factors, potentially leading to unexpected inverter behavior and operational challenges in grids with high PV penetration. This study underscores the importance of re-evaluating conventional testing methods and incorporating Power Hardware-in-the-Loop structures to achieve test results that more closely align with real-world conditions.