A current limiting strategy for grid-forming converters based on voltage deviation adaptive virtual impedance

• A voltage-based adaptive virtual impedance control method. • A control method to adaptively reduce the active power reference value. • Analysis of the impact of the proposed method on transient stability. • Quantitatively design the adjustment coefficient of the virtual impedance. Grid-forming (GFM) converters face the risk of saturation under large disturbances, which will degrade the stability performance of the system. Most existing adaptive virtual impedance methods generate virtual impedance based on current limit values. However, such approaches tend to exhibit significant fluctuations, making it difficult to effectively suppress transient inrush currents during fault occurrence and clearance. To address this issue, this paper comprehensively considers transient stability, steady-state fault current suppression, and transient inrush current limitation. Firstly, a transient stability enhancement adaptive control strategy accounting for line resistance is proposed. By adaptively adjusting the active power reference value, this strategy not only enhances the transient stability of GFM converters but also effectively suppresses the steady-state fault current. Subsequently, a voltage-based adaptive virtual impedance control method is proposed to suppress transient inrush currents, and its impact mechanism on transient stability is analysed. The study reveals that even if the adaptive virtual impedance is active only during the brief transient period, an excessively large virtual impedance may still trigger irreversible transient instability. Therefore, by integrating the analytical method and the phase portrait method, this paper determines the critical boundary values for the adaptive virtual impedance adjustment coefficient, ensuring that transient inrush currents are limited within the allowable range of power devices, without inducing transient instability due to excessive virtual impedance. Finally, the effectiveness of the proposed control strategies is verified based on the simulations and the hardware-in-the-loop experiments.