Photovoltaic inverter islanding detection method

The invention discloses a method for detecting an island of a photovoltaic grid-connected inverter. The method comprises the following steps of: 1), detecting a voltage frequency at a common coupling point of the inverter and a power grid, wherein when the voltage frequency is between f11 and f12, a phase position of output current of the inverter is the same to that of voltage at the coupling point; and, by modifying the phase position between the output current of the inverter and the voltage at the coupling point, compared with the voltage at the coupling point, the output current is ahead of time in theta degrees (when fgrid is more than f12 and less than f22) or lags in theta degrees (when fgrid is more than f21 and less than f11); and 2), to compensate a dead zone appeared in frequency detection, judging whether an island effect exists by modifying an amplitude value of the output current of the inverter within one power frequency period after every four power frequency periods and recovering the amplitude value of the output current into an original value after the period. According to the method, harmonic waves output by the inverter to the power grid can be effectively reduced; the detection time is short; the calculation method is simple; and the computing resource of a control chip can be saved.