Processing sinewave signals of variable frequency in a device with fixed processing rates

A method comprising:

• obtaining, via an intelligent electronic device (IED), electrical measurements of an input signal of a power system, wherein the electrical measurements are obtained at a sampling frequency and the input signal is indicative of an operating frequency of the power system;
• generating an intermediate signal by multiplying the input signal with quadrature signals, wherein the intermediate signal has a direct current (DC) component indicative of a magnitude and a phase of the input signal;
• storing the intermediate signal comprising in phase and quadrature components in a first-in-first-out (FIFO) buffer;
• and
• filtering, via the IED, the intermediate signal using an adjustable length rounded-corner boxcar filter comprising a plurality of taps to generate the magnitude and the phase of the input signal, wherein a length of the adjustable length rounded-corner boxcar filter varies based at least in part on a period measurement of the power system, and wherein end taps of the plurality of taps are interpolated to a lesser value than all other taps of the plurality of taps.

A tangible, non-transitory, computer-readable medium comprising instructions, wherein the instructions, when executed by processing circuitry, are configured to cause the processing circuitry to perform operations comprising:

• obtaining electrical measurements of an input signal of a power system, wherein the electrical measurements are obtained at a sampling frequency and the input signal is indicative of an operating frequency of the power system;
• generating an intermediate signal from the input signal by multiplying quadrature signals with the input signal, wherein the intermediate signal has a direct current (DC) component indicative of a magnitude and a phase of the input signal;
• storing the intermediate signal comprising in phase and quadrature components in a first-in-first-out (FIFO) buffer;
• and
• filtering the intermediate signal using an adjustable length rounded-corner boxcar filter comprising a plurality of taps to obtain the magnitude and the phase of the input signal, wherein a length of the adjustable length rounded-corner boxcar filter varies based at least in part on a period measurement of the power system, and wherein end taps of the plurality of taps are interpolated to a lesser value than all other taps of the plurality of taps.