Time alignment method of differential protection device, differential protection device and differential protection system

A differential protection device for a power line, wherein the differential protection device is configured to:

• obtain, from a merging unit of the power line, a plurality of current sampled values of the power line and a count value of each of the plurality of current sampled values, a sampling moment of a current sampled value whose count value is a first value in the plurality of current sampled values is a moment of generation of a pulse per second (PPS) signal of a satellite positioning module of the merging unit;
• resample the plurality of current sampled values according to a sampling frequency of J points/cycle of the differential protection device to obtain a plurality of current resampled values, the plurality of current resampled values comprises a reference current resampled value corresponding to the current sampled value whose count value is the first value, wherein J is an integer greater than 1;
• perform a Fourier transform on the plurality of current resampled values to obtain a plurality of temporally arranged current Fourier values, wherein the plurality of temporally arranged current Fourier values comprises (i) at least one set of current Fourier values each comprising G current Fourier values, a first current Fourier value of the each set of current Fourier values is used as a reference current Fourier value, where G is an integer greater than 1, and (ii) a reference current Fourier value corresponding to the sampling moment of the current sampled value whose count value is the first value in the plurality of current sampled values, wherein the reference current Fourier value is determined based on the reference current resampled value and the J−1 current resampled values that temporally arranged before the reference current resampled value, and wherein the differential protection device is configured to perform the Fourier transform on the plurality of current resampled values by:
• taking the reference current resampled value and J−1 current resampled values that are temporally arranged before the reference current resampled value as a transform object for the Fourier transform to obtain the first current Fourier value of the set of current Fourier values as the reference current Fourier value;
• and
• performing the Fourier transform G−1 times iteratively to obtain the second to G-th current Fourier values of the set of current Fourier values, wherein each of G−1 Fourier transforms is performed by taking J current resampled values obtained by moving K current resampled values backward in time from the transform object for the previous Fourier transform, wherein G=[M/K] and [M/K] is a carry out round-down operation on M/K;
• and
• initiate a differential protection action for the power line based on the temporally arranged current Fourier values.

A differential protection device for a power line, wherein the differential protection device is configured to:

• obtain, from a merging unit of the power line, a plurality of current sampled values of the power line and a count value of each of the plurality of current sampled values, a sampling moment of a current sampled value whose count value is a first value in the plurality of current sampled values is a moment of generation of a pulse per second (PPS) signal of a satellite positioning module of the merging unit;
• resample the plurality of current sampled values according to a sampling frequency of J points/cycle of the differential protection device to obtain a plurality of current resampled values, the plurality of current resampled values comprises a reference current resampled value corresponding to the current sampled value whose count value is the first value, wherein J is an integer greater than 1;
• perform a Fourier transform on the plurality of current resampled values to obtain a plurality of temporally arranged current Fourier values, wherein the plurality of temporally arranged current Fourier values comprises (i) at least one set of current Fourier values each comprising G current Fourier values, a first current Fourier value of the each set of current Fourier values is used as a reference current Fourier value, where G is an integer greater than 1, and (ii) a reference current Fourier value corresponding to the sampling moment of the current sampled value whose count value is the first value in the plurality of current sampled values, wherein the reference current Fourier value is determined based on the reference current resampled value and the J−1 current resampled values that temporally arranged before the reference current resampled value, and wherein the differential protection device is configured to perform the Fourier transform on the plurality of current resampled values by:
• taking the reference current resampled value and J−1 current resampled values that are temporally arranged before the reference current resampled value as a transform object for the Fourier transform to obtain the first current Fourier value of the set of current Fourier values as the reference current Fourier value;
• and
• performing the Fourier transform G−1 times iteratively to obtain the second to G-th current Fourier values of the set of current Fourier values, wherein each of G−1 Fourier transforms is performed by taking J current resampled values obtained by moving K current resampled values backward in time from the transform object for the previous Fourier transform, wherein G=[M/K] and [M/K] is a carry out round-down operation on M/K;
• and
• initiate a differential protection action for the power line based on the temporally arranged current Fourier values;
• and
• wherein the differential protection device is configured to tag the moment of each current Fourier value of the plurality of current Fourier values by applying the following operations on each set of current Fourier values:
• tagging a moment of the reference current Fourier value of the set of current Fourier values as the sampling moment of the current sampled value which corresponds to the reference current Fourier value and has count value of the first value;
• tagging a moment of the Q-th current Fourier value of the set of current Fourier value as the moment of the reference current Fourier value plus ((Q−1)*Δt, wherein the Q is an integer greater than 1 and not greater than G, and the Δt=(duration of 1 cycle)/(J/K);
• and
• stop obtaining the current Fourier values of the set of current Fourier value that has not yet been obtained and obtaining the reference current Fourier value of the subsequent set of current Fourier values relative to the set of current Fourier value, in response to receive a current sampled value which corresponds to the reference current Fourier value of the subsequent set of current Fourier values and has count value of the first value.