Reduce of the acoustic noise effect from PWM-VSI inverter controlled AC-drives by music and random modulation

PWM-VSI inverter driven AC-machines emit acoustical noise. The authors present a combined modulation strategy which uses the acoustical noise for playing a melody in combination with random modulation and stator flux oriented asynchronous vector modulation (SFAVM) in order to reduce the effect of the acoustical noise. The relationship between notes and switching frequencies is discussed as well as the duration of a note. A computer program converts notes from a melody to a modulation file which easily can be implemented in a microcontroller. The modulation strategy is tested in a high performance AC-drive system. A test shows it is possible to activate tones in a melody from an AC-machine by varying the switching frequency. The best effects are obtained at two times the switching frequency. Tests also show that tones have optimum effect at lower speed as well as they show that random modulation reduce the acoustic noise effectively. Random modulation uncovers some mechanical resonant frequencies. Finally, it is demonstrated that music modulation is easy to implement and cost a minimum of ROM and can be a new benefit in combination with random and SFAVM modulation for AC-drives in the future.<>