Photovoltaic grid-connected tie line pilot protection method based on negative sequence current amplitude ratio

The invention discloses a photovoltaic grid-connected tie line pilot protection method based on a negative sequence current amplitude ratio. The method comprises the following steps: presetting three-phase current data on two sides of a grid-connected tie line in a sampling period after a photovoltaic grid-connected tie system fails; negative-sequence currents on the two sides of the photovoltaic grid-connected tie line are calculated through a Fourier algorithm and a symmetric component method; comparing whether the negative sequence current values and the amplitude current values at the two sides of the line are larger than a negative sequence current setting value or not, and if yes, judging an external fault; if yes, the amplitude ratio of the negative-sequence current on the system side to the negative-sequence current on the station side is obtained; judging whether the amplitude ratio is greater than a protection setting value or not; and if the protection setting value is greater than the protection s