Measurement of Voltage Fluctuation and Flicker Based on Coherent Demodulation with Synchronous Digital Carrier

Square demodulation and Root Mean Square (RMS) demodulation are noncoherent detections which are used in voltage fluctuation and flicker measurement. There are doubled frequency of the modulation signal and intermodulation distortion in the product of the square demodulation. The magnitude-frequency characteristic of RMS demodulation drops obviously with the increase of frequency of the modulation signal, the magnitude of the output has distinct difference although the modulation signal has the same fluctuation amplitude and different frequency. Coherent detection of voltage fluctuation and flicker based on synchronous digital carrier is proposed, the performance requirement of the anti-aliasing filter is depressed by over sampling, it makes the system easy to realize, digital filter blocks the elements whose frequency are greater than the flicker-fusion threshold, and there is no doubled frequency of the modulation signal and intermodulation distortion, theoretical analysis and simulation waveform show that the measuring accuracy of the new approach is superior to the other two´s.