Improved spectral performance of SPWM inverter based on the time-sequence of chaos

A novel approach for improving the spectral performance of sinusoidal Pulse Width Modulation (SPWM) inverter is presented. By varying the carrier frequency according to chaotic time-sequence, the discrete spectrum of the output voltage is transformed into the continuous spectrum, which could reduce the acoustic noise concentrated at specific tones in an inverter-driven electric machine. Fourier analysis shows that the harmonic at the fixed frequency has been restrained effectively and the distribution of the spectrum is in a wider range. Besides, a novel variable is introduced for the evaluation of the output voltage spectrum in SPWM inverter. Simulations and experiments with DSP confirm the advantages of the novel approach. Experimental results show the annoying acoustic noise has been translated into some enjoyable sound like a fall or water flowing when this novel method is applied.