The grid-forming (GFM) converter is the trend and a promising solution for low-inertia and weak grids. Traditional GFM converters employ a current limit strategy to prevent the risk of overcurrent. However, the current limit strategy will lead to unstable issues when larger disturbances occur, such as large frequency and voltage drops. Furthermore, unlike high-voltage transmission grids, the resistive feature is more pronounced in low-voltage distribution grids, which can lead to an overvoltage issue. Therefore, this paper proposes an improved voltage regulation method for the GFM converter, where a Lyapunov-based grid-impedance estimator is developed to obtain the grid inductance and resistance, enabling the proposed method to adapt to different X/R ratios. The proposed method can alleviate overvoltage problems in GFM converters under low X/R ratio conditions. The simulation results are given to prove the effectiveness of the proposed method.

Grid-following control (GFL) has been widely implemented as the dominant control method for inverter-based resources (IBR). However, because GFL cannot provide sufficient inertia for frequency regulation, grid-forming control (GFM) is proposed as an alternative solution. However, the impact of grid dynamics characteristics on GFL and GFM control is rarely discussed. Therefore, this paper systematically derives and compares the frequency response of GFL and GFM control, considering the grid dynamics that are emulated by a synchronous generator. The impact of the inertia of GFM is investigated by pole-zero maps.

Highly self-sufficient energy hubs offer a promising solution to mitigate grid congestion in favor of grid operators and to reduce grid fees for the benefit of energy hub operators. Meanwhile, the energy hub's capacity may far exceed the grid connection capacity, creating a weak grid situation. As a result, power quality issues such as voltage fluctuations, frequency deviations, and even instability may occur. In this work, a grid-forming energy storage system (GFM-ESS) is integrated to address these potential problems. A model of the GFM-ESS and energy hub is established based on a 50 kW PV-Hydrogen energy hub demonstrator, where PV-generated power is utilized for green hydrogen production. A trade-off design is proposed to identify the optimal balance between the capacity of the GFM-ESS and the grid connection. The voltage and frequency response at the hub's bus are analyzed to evaluate this trade-off. While experiments with the 50 kW demonstrator are ongoing, simulation results are provided to validate the effectiveness of the proposed design.