Frequency measurement device, frequency measurement method and under frequency load shedding device

A frequency measurement device, comprising:

• a sampling module unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency input thereto;
• an angle shift computation unit based on single-cycle Discrete Fourier Transform DFT that computes and outputs a first angle shift based on the single-cycle DFT, in accordance with the voltage sampling value input from the sampling module unit;
• an angle shift computation unit based on multi-cycle DFT that computes and outputs a second angle shift based on the multi-cycle DFT, in accordance with the voltage sampling value input from the sampling module unit;
• an angle shift selection unit that selects and outputs one of the first angle shift and second angle shift a absolute value of which is smaller as a selected angle offset, in accordance with the first angle shift and second angle shift input thereto;
• a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset input thereto, and outputs the sampling frequency to the sampling module unit as a new sampling frequency;
• and
• a frequency measurement value computation and outputting unit that computes and outputs a frequency measurement value in accordance with the selected angle offset input thereto.