Phase sequence judgment method for three-phase alternating current

The invention relates to a phase sequence judgment method of three-phase alternating current, which comprises the following steps: sampling three-phase alternating current voltage in real time, comparing real-time sampling values pairwise, dividing into three areas which are repeated and named as 1, 2 and 3 respectively, after the real-time sampling values are compared pairwise and enter a certain area, firstly detecting the value of a global variable PSJ in the area, and then determining the phase sequence of the three-phase alternating current. If the value in the global variable PSJ is 0, assigning the name of the region to the global variable PSJ, and if the value in the global variable PSJ at the moment is 3 and the name in the region is 2, judging that the phase sequence of the three-phase alternating current is a positive sequence; and if the value in the global variable PSJ is 2 and the name in the region is 3, the phase sequence of the three-phase alternating current is judged to be an inverted seque