• A novel NPLL-based Mode Transition Mechanism (NPLL-MTM) is proposed for autonomous operation and parallel inverter action in AC/DC microgrids. • A dual-controller architecture combining voltage and current control ensures seamless operation in both islanded and grid-connected modes. • A SOGI–VSM droop-based control strategy enhances dynamic stability by providing virtual inertia and accurate phase angle estimation. • The adaptive vectorial filter (AVF) improves power quality by extracting fundamental current components and offering reactive power support. • The NPLL-MTM enables a smooth transition between control modes, ensuring reliable load and storage management during islanded operation. • Experimental SPARTAN-6 FPGA validation of a PV–battery microgrid confirms IEEE 519/2030.7 compliance, outperforming PLL and current control. This paper addresses a pressing concern in hybrid AC/DC microgrids in achieving stable, seamless transitions between grid-following and islanded operations of parallel inverters. Autonomous control with power-quality assurance and reliable synchronization are imperative for future resilient distributed energy systems. To develop technology that responds to the above needs, a new mode transition mechanism based on a phase-locked loop (NPLL-MTM) is proposed, in conjunction with a dual controller strategy that incorporates current and voltage control loops. In grid-following operation, a combination of the second-order generalized integrator (SOGI) and virtual synchronous machine droop (VSM-droop) controller enhances phase estimation, providing virtual inertia support and dynamic response. In parallel, the adaptive vectorial filter (AVF) supports an improved fundamental current extraction and compensating for reactive power. In islanded operations, the NPLL-MTM guarantees a smooth current-to-voltage control transition to keep load demand and system stable. The simulation and practical validation of the proposed methodology was carried out on a SPARTAN-6 FPGA–based PV–battery microgrid prototype. The results showed a reduction of grid current THD from 12.6% to 1.25% within IEEE-519 limits, while voltage and frequency were maintained within ± 10% p.u., and 2–4% conforming to IEEE-2030.7. The experimental effort allowed securing islanding within 2 s and resynchronization within 1–2 cycles. Comparative evaluations have shown improved transient response, accuracy in power sharing, and reliability in transitions compared to the conventional PLL-based approaches. These results endorse the proposed method as an exceptionally convincing means of guaranteeing the smooth, standard-compliant, and practically realizable operation of hybrid microgrids with high performance.
Sahoo et al. (Tue,) studied this question.