Abstract: The present disclosure discloses methods for sensing a cycle and a phase difference of an AC signal. A method for sensing the cycle of an AC signal may comprise the steps of: determining sample points in waveforms of the AC signal according to a fixed time interval; sampling N continuous sample points as one group of initial samples, in which the product of N and the fixed time interval is larger than or equal to the minimum cycle of the AC signal; sampling a plurality of groups of samples as a plurality of groups of target samples; calculating the cross-correlation between each group of the plurality of groups of target samples and the group of initial samples; and providing the time interval between the group of initial samples and a group of the target samples that has the highest cross-correlation as the cycle of the AC signal.