Extraction of Common-Mode Impedance of an Induction Motor by Using All-Phase FFT With Intermediate-Frequency Filtering

This letter proposes an online extraction method of common-mode (CM) impedance of induction motor based on all-phase spectrum calculation. All-phase fast Fourier transform with intermediate-frequency filtering (ApFFTIF) is proposed based on infinite impulse response filter, zero-phase filtering technique, and all-phase fast Fourier transform. By using ApFFTIF, the accurate amplitude spectrum together with accurate phase spectrum of CM impedance of induction motor are extracted. Then genetic algorithm is used to establish the model of CM impedance of inductor motor. Finally, through comparing CM impedances extracted by using different spectrum calculation methods, and through comparing measured and calculated CM currents, the accuracy of the proposed method is validated.