Enhanced Low-Voltage Ride-Through Scheme for Grid-Forming Converters Considering Current Limitation and Transient Stability Simultaneously

Grid-forming (GFM) converters face significant challenges in low-voltage ride-through (LVRT) due to their limited overcurrent capacity. Various transient current-limiting methods have been proposed to address this issue. However, simple current-limiting settings during grid faults can severely compromise the transient stability and reactive power output of GFM, thereby affecting compliance with grid codes. To align with the global push for sustainable energy systems, this study proposes a virtual impedance tuning method (CL-TS VI) that simultaneously considers current-limiting and transient stability requirements, addressing the dual demands of high efficiency and reliable integration of renewable energy. By combining this method with an inner-loop control design based on balanced currents, an enhanced low-voltage ride-through (E-LVRT) scheme is developed. The proposed scheme achieves the coordinated fulfillment of both current-limiting and transient stability requirements by quantitatively analyzing the applicable range of virtual impedance parameters. Specifically, under the constraint of current-limiting conditions, fault scenarios are classified into two categories, with and without equilibrium points, depending on the severity of voltage sag. Then, based on the Lyapunov stability theory, separate virtual impedance design criteria are proposed for these two scenarios, ensuring that the GFM maintains both current-limiting capability and transient stability during fault ride-through while minimizing active power losses. Additionally, the proposed scheme enhances reactive power support capability in the post-fault phase, ensuring compliance with grid code requirements while promoting sustainable grid operation. The proposed strategy is validated through time-domain simulations and hardware experiments. The results demonstrate that the proposed scheme significantly improves the transient stability of GFM and provides a reliable solution for its efficient operation under complex grid conditions.