Acoustic noise reduction in sinusoidal PWM drives using a randomly modulated carrier

Acoustic noise in an inverter-driven AC electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse-width modulation) is to cause the switching pattern to be random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in sinusoidal PWM (pulse-width modulation) with bandlimited white noise. All the advantages of sinusoidal PWM are preserved with this technique. These include real-time control, linear operation, good transient response, and a constant average switching frequency. By controlling the bandwidth and RMS value of the pink noise modulation, it is shown that the instantaneous variation in switching frequency as well as the bandwidth of the energy spectrum in the machine can be specified within predetermined limits. Experimental results show the absence of acoustic noise concentrated at specific tones which is present with conventional sinusoidal modulation