Transient fault-current characteristics and second-order equivalent modeling of grid-following converters under low-voltage ride-through

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This paper investigates the transient fault-current behavior of grid-following converters in distribution networks during low-voltage ride-through (LVRT) under an inner-current and outer-power control architecture. A second-order equivalent model is derived by coupling the inner-loop PI controller with the converter circuit dynamics, clearly showing how the natural frequency and damping ratio depend on the proportional (Kp) and integral (Ki) gains. To incorporate engineering practices, reactive-power priority with a 1.2 pu current limit is considered, and we propose an amplitude-slope unified reachability constraint for reference generation and feasibility assessment. Comparative studies on a 10-kV system demonstrate strong agreement between PSCAD simulations under overdamped conditions and the proposed model, establishing applicability boundaries across underdamped, critically damped, and overdamped regimes. Based on these findings, practical tuning guidelines are provided for LVRT, ai ding relay protection settings and grid-connection control parameterization.

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