Implementation and test of a digital quasi-random modulated SFAVM PWM in a high performance drive system

The authors propose a modulation scheme for reducing the acoustic noise effect from an AC machine which can be implemented digitally. The scheme is based on a stator flux asynchronous vector modulation (SFAVM) imposed by a digital bandlimited white noise generator. The modulation strategy is tested in a 1 kVA high-performance 16 b microprocessor controlled AC drive system. Fast Fourier transform spectra on the line-line voltage and the acoustic noise are presented, and it is shown that the new modulation strategy can decrease the noise effect. The stator flux polygon and the line current are measured, and the random modulation strategy is demonstrated. The total sound pressure level from the AC machine is investigated with fixed switching frequencies and with different random modulated frequency spans. It is concluded that a properly chosen fixed switching frequency has the lowest total sound pressure level. However, the random modulation strategy distributes the noise frequencies, and the noise is much more comfortable and less annoying