The invention discloses an active island detection method and
system based on
harmonic impedance characteristic identification, and the method comprises the steps: analyzing the
harmonic impedance difference of grid-connected points in a grid-connected state and an
island state, and building a state criterion based on resonant
frequency deviation and impedance amplitude through the comparison of the
frequency response characteristics of island impedance and grid-connected impedance; fitting the
grid impedance into an RLC parallel model in a selected
frequency band, and mapping the topological difference of the
power grid into a parameter difference; embedding a low-
voltage ride-through strategy in the control of the
voltage source converter, and adjusting reactive current in a grading manner according to the
voltage drop degree of a grid-connected point; fundamental
waves and
harmonic waves are separated through a
cascade notch filter, two synchronous harmonic
waves are injected into the
system through
constant current control, and it is ensured that injection signals of a multi-
voltage source converter are in the same phase in a
phase locking link; and solving an overdetermined equation set based on the double-
frequency response data to identify RLC parameters, setting an island criterion, and synchronously completing island judgment in a low-voltage ride-through time window. Detection precision is improved, dynamic response is optimized, and power generation efficiency is improved.