An integrated controller to perform LVRT operation in PV systems connected to a LV grid during balanced and unbalanced faults

For high PV penetration, grid ancillary services such as dynamic voltage support and low-voltage ride-through (LVRT) operation are recommended by network operators. This paper proposes an integrated controller for LVRT capability of a three-phase grid-tied PV system connected to a LV grid. Generally X/R ratio is low for LV grids, therefore the active power injection is given higher priority than the reactive power injection during grid faults. The proposed controller includes a) reactive power support with active power curtailment (RPS-APC) controller for dynamic grid support, b) decoupled double synchronous reference frame (DDSRF) based positive and negative sequence extractor, c) dual synchronous reference frame (DSRF) based current controller for unbalanced current injection, d) peak current limiter to regulate the current within inverter rating, and e) modified protections based on LVRT curve. The performance of the integrated controller under different symmetrical and unsymmetrical grid faults is evaluated and simulation results are provided.