Compared with power frequency measurement, in principle, frequency conversion is mainly to improve the test bandwidth. In actual measurement, because there are no national standards and specifications for frequency conversion measurement, the technical indicators of the measured products, especially the sensors claimed to be suitable for frequency conversion measurement, are often incomplete and cannot be traced back.
Among them, the unclear phase error of voltage and current sensors is the main reason for the inaccurate measurement of variable frequency power.
If you write a graduation thesis, the above situation should be highlighted. For more details, please refer to the related articles in my library!
As for the design of the measuring device, under the condition of ignoring the above shortcomings of the sensor (it is estimated that the teacher did not consider these situations).
Choose a reasonable sampling frequency mainly according to the signal bandwidth, generally above 100kHz.
The fundamental effective value and fundamental phase difference of voltage and current can be obtained by FFT transform and calculated according to related formulas.