Anti-islanding scheme of grid-connected inverter is a key function of standards compliance,
since unintentional islanding results in safety hazards, reliability, and many other issues.
Therefore, many anti-islanding schemes have been researched, however, most of them have
problems, which deteriorate performance of islanding detection under parallel-operation.
Therefore, this paper proves the reason of problems and proposes a new anti-islanding scheme
that has precise islanding detection under parallel-operation in single-phase and three-phase
system. Finally, both simulation and experimental result validate the proposed scheme.