Three-phase AC phase sequence detecting method and apparatus

A three-phase AC phase sequence detecting method, including the steps of:

• 1) sampling instant values of a three-phase AC electrical signal in real-time to obtain a set of instant values;
• 2) converting, using coordinate conversion, said set of instant values into electrical signal components in a two-phase still coordinate system;
• 3) performing an arc tangent calculation on the electrical signal components to obtain an output signal value corresponding to a sampling timing;
• 4) executing step 1) to step 3) one or more times, to obtain one or more output signal values corresponding to one or more sampling timings adjacent with said sampling timing at step 3);
• 5) combining the output signal values obtained from step 3) and the one or more output signal values obtained from step 4) to form one periodic function, which is a linear function within one minimum positive period, and the period of the periodic function is the same as that of the three-phase AC electrical signal, determining the three-phase AC phase sequence to be positive or negative based on whether the periodic function is an increasing or a decreasing function within one minimum positive period:
• if the periodic function is an increasing function within one minimum positive period, the three-phase AC phase sequence is determined to be positive sequence;
• if the periodic function is a decreasing function within one minimum positive period, the three-phase AC phase sequence is determined to be negative sequence,
• wherein the waveform between two adjacent peaks in the waveform of any phase in three-phase AC electrical signal corresponds to one minimum positive period.