Experimental comparison of conventional and bus-clamping PWM methods based on electrical and acoustic noise spectra

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 technique used to modulate the inverter is the key factor determining the magnitude of current harmonics. Bus-clamping 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 6 kW induction motor drive. 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. Comparison of the experimental results show that the magnitude of dominant acoustic noise component around the carrier frequency is reduced significantly with BCPWM methods, compared to CSVPWM, at high modulation indices.