Research On Inter Harmonic Detection Method Based On Zoom FFT

The improving the quality of power supply and economical operation of power system depends on the accurate and real-time detection of harmonic voltage.But the existing of inter harmonic make the detection of harmonic become difficulty. Inter harmonic is a kind of harmonic which is not an integer of the fundamental frequency component. Not like harmonic, the inter harmonic can't be measured accurately by single period fast Fourier transform. In order to get the accurate spectrum of voltage the sample time must extended. Extension sampling time will cause significant increasing of calculation. This makes very big difficulty to the real-time power quality monitoring system. The Zoom FFT method can slake this detect. When the Zoom FFT is implement, the interesting frequency band is moved to the zero by complex multiplication, a low pass filter is used to avoid the spectrum leak, the filtered data is resample and get a short samples. By this way the Zoom FFT method can get the high frequency resolution in the interesting frequency band and low frequency resolution in the other frequency band. Through this methods can enhance the accurate of harmonic measurement without large increasing of calculation. In order to test this method the Matlab is used to simulation the inter harmonic of power system, the FFT and Zoom FFT is implement at the same time to detect these inter harmonic. The simulation prove the Zoom FFT method can detect the inter harmonic accurate.