Comparative evaluation of SRF-PLL and instantaneous-power LVRT control for a three-wire grid-connected PV system under ground faults

The performance of low voltage ride-through (LVRT) control depends on the voltage information used for synchronisation and current-reference generation, as well as the physical current paths of the converter. In this paper, four synchronous reference frame phase-locked loop (SRF-PLL) and instantaneous power theory (IPT) implementations are compared on a common 1.504 MW photovoltaic simulation model under single line-to-ground and double line-to-ground faults. The three-wire converter is connected through a delta–grounded-wye transformer. Consequently, its zero-sequence line current is constrained to zero, although ground-fault current is present on the grounded transformer side. The current-control action is therefore confined to the two independent converter axes. The comparison uses conventional and positive-sequence-conditioned SRF and IPT implementations with a shared reactive-current-priority LVRT law, DC-voltage regulation and current-reference limits. For the double line-to-ground case, positive-sequence IPT provides 730.6 kvar at the low-voltage measurement point, compared with 376.1 kvar for instantaneous-voltage IPT, while its nonfundamental current residual decreases from 22.06% to 0.037%. However, the latter controller has a smaller 100 Hz active-power component, demonstrating a trade-off between power oscillation and current quality. Actual transient current reaches 1.234 pu despite a 1.2 pu reference ceiling. Sequence-extraction diagnostics against established DSOGI and DSC methods, together with transformer-side measurements, explain these outcomes. Hardware-in-loop captures document laboratory-platform observations; all quantitative controller comparisons are based on simulations.