Improved microgrid performance with virtual synchronous machine-droop control and seamless transition using phase locked loop-based islanding detection scheme

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.