Bi-Functional Non-Superconducting Saturated-Core Inductor for Single-Stage Grid-Tied PV Systems: Filter and Fault Current Limiter

Abstract

Single-stage grid-interfaced PV topologies have challenges with high grid fault currents, despite being more efficient, simpler to implement, and less expensive than two-stage ones. In such systems, a single inverter is required to perform all grid-interface tasks. i.e., maximum power point tracking (MPPT), DC voltage stabilization, and grid current control. This necessitates a hardware-based fault current limitation solution rather than a software-based one to avoid adding to the inverter’s control complexity and to mitigate the implications of PV system tripping. Therefore, in this study, a dual-functional non-superconducting saturated-core inductor-based (SCI) reactor is proposed to be applied at the output of a single-stage PV inverter. It involves two operation modes: a grid pre-fault mode where it filters the line current, hence minimizing its THD, and a grid-fault mode where it acts as a fault current limiter (FCL). Controlling the DC saturation current flowing into its control winding terminals alters the core magnetization of the SCI to vary its impedance between a low value during normal utility operation and a maximal value during faults. Consequently, the system is protected against inverter failures or unnecessary circuit-breaker tripping, which preserves service continuity and reduces system losses. Moreover, compared to existing FCLs, the proposed topology is an appealing candidate in terms of cost, size, reliability, and harmonic filtering ability. The bi-functionality and usefulness of the proposed reactor are confirmed using simulation and experimental results.