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This paper presents an experimental procedure to determine the acoustic and vibration behavior of an inverter fed induction motor based on measurements of current spectrum, acoustic noise spectrum, overall noise in dB, and overall Aweighted noise in dBA. Measurements are carried out on spacevector modulated 8-hp and 3-hp induction motor drives over a range of carrier frequencies at different modulation frequencies.The experimental data helps to distinguish between regions of high and low acoustic noise levels. The measurements also bring out the impact of carrier frequency on the acoustic noise. The sensitivity of the overall noise to carrier frequency is indicative of the relative dominance of the high-frequency electromagnetic noise over mechanical and aerodynamic components of noise. Based on the measured current and acoustic noise spectra, the ratio of dynamic deflection on the stator surface to the product of fundamental and harmonic current amplitudes is obtained at each operating point. The variation of this ratio of deflection to current product with carrier frequency indicates the resonant frequency clearly and also gives a measure of the amplification of vibration at frequencies close to the resonant frequency. This ratio is useful to predict the magnitude of acoustic noise corresponding to significant time-harmonic currents flowing in the stator winding.

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The acoustic noise emitted by an induction motor, powered by a voltage source inverter, is an environmental issue. Harmonics present in the stator current are the main reason for the increased acoustic noise in motor drives. The pulse-width modulation (PWM) technique used to modulate the inverter is a key factor determining the magnitude of current harmonics. Busclamping pulse-width modulation (BCPWM) techniques have got much attention nowadays due to reduced switching loss, compared to conventional space vector PWM (CSVPWM). In this paper, two BCPWM techniques namely, 60 • and 30 • BCPWM methods are compared with CSVPWM on the basis of electrical spectra as well as acoustic noise spectra. Experiments are conducted on a pulse-width modulated voltage source inverter fed induction motor drives. Harmonic analysis is carried out on the measured line to line voltage, stator current and acoustic noise, corresponding to the three methods, at different fundamental and carrier frequencies. Based on the magnitude and phase of current harmonics, the frequency and normalized magnitude of dominant magnetic force waves are predicted theoretically. Theoretical predictions and experimental results both show that the magnitudes of dominant acoustic noise components around the carrier frequency are reduced significantly with these BCPWM methods, compared to CSVPWM. Further, it is shown that 30 • BCPWM is better than 60 • BCPWM in terms of acoustic pleasantness.

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