Abstract: The present disclosure relates to a method for motor thermal overload protection, including: obtaining a motor thermal limit curve; selecting a first and a second overload factor calculation point on the curve, and calculating the first and second overload factors based on a preset heating time constant; calculating a modified overload factor based on the first and second overload factors; selecting at least two time constant calculation points on the motor thermal limit curve, and calculating a modified heating time constant for each time constant calculation point based on the modified overload factor; obtaining a modified heating time function for each motor operating point based on the modified heating time constant for each time constant calculation point; calculating a stator heat level at each motor operating point based on the modified overload factor and heating time function; comparing the stator heat level with the first and second predetermined thresholds.

Abstract: A frequency measurement method is provided, which comprising: sampling a voltage to be measured with a fixed sampling frequency; obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a discrete Fourier transform (DFT) calculation; obtaining a frequency offset amount by using the positive-sequence voltage angle change amount; and obtaining a frequency-related measurement value by using the frequency offset amount. A frequency measurement apparatus is also provided. measurement value. This frequency measurement method does not require iterative calculations, and directly obtains frequency-dependent measurement values, thereby responding quickly to frequency changes. In addition, a frequency measurement apparatus is also provided.

Abstract: The present invention provides method, apparatus, and computer readable storage medium for an electrical islanding detection. The method for electrical islanding detection method includes: receiving a three-phase voltage in an electrical power system; for the three-voltage voltage, calculating a voltage angle sudden-change of each phase, respectively; determining whether an absolute value of the voltage angle sudden-change of each phase is greater than a first angle sudden-change setting value; determining whether directions of the voltage angle sudden-changes of three phase are the same if the absolute value of the voltage angle sudden-change of each phase is greater than the first angle sudden-change setting value; and determining that the electrical islanding appears if the directions of the voltage angle sudden-changes of the three phases are the same.

Abstract: A frequency measurement method is provided, which comprising: sampling a voltage to be measured with a fixed sampling frequency; obtaining a positive-sequence voltage angle change amount for a predetermined operation interval time by using a sampling sample obtained by the sampling and based on a discrete Fourier transform (DFT) calculation; obtaining a frequency offset amount by using the positive-sequence voltage angle change amount; and obtaining a frequency-related measurement value by using the frequency offset amount. A frequency measurement apparatus is also provided. measurement value. This frequency measurement method does not require iterative calculations, and directly obtains frequency-dependent measurement values, thereby responding quickly to frequency changes. In addition, a frequency measurement apparatus is also provided.

Abstract: A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same 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.

Abstract: The present invention provides method, apparatus, and computer readable storage medium for an electrical islanding detection. The method for electrical islanding detection method includes: receiving a three-phase voltage in an electrical power system; for the three-voltage voltage, calculating a voltage angle sudden-change of each phase, respectively; determining whether an absolute value of the voltage angle sudden-change of each phase is greater than a first angle sudden-change setting value; determining whether directions of the voltage angle sudden-changes of three phase are the same if the absolute value of the voltage angle sudden-change of each phase is greater than the first angle sudden-change setting value; and determining that the electrical islanding appears if the directions of the voltage angle sudden-changes of the three phases are the same.

Abstract: A frequency measurement device includes a sampling unit that outputs a voltage sampling value in accordance with a voltage to be sampled and a sampling frequency; an single-cycle DFT angle shift computation unit that computes and outputs a first angle shift in accordance with the voltage sampling value; an multi-cycle DFT angle shift computation unit that computes and outputs a second angle shift in accordance with the voltage sampling value; a selection unit that selects and outputs one of the first and second angle shifts as a selected angle offset; a sampling frequency computation and outputting unit that computes a sampling frequency in accordance with the selected angle offset and outputs the same 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.