Digital implemented random modulation strategies for AC and switched reluctance drives

This paper describes digital based random modulated PWM strategies and different implementation techniques for AC-machines and switched reluctance machines. The aim of random modulation strategies is to reduce the emitted acoustical noise. The discussed techniques are online calculation of random values, look-up tables, random leading-lagging edge modulation and random angle control of switched reluctance machines. Measurements on the voltage and acoustic spectra show some of the benefits in the implementation techniques on different load systems. An intelligent distributed modulation technique is also discussed which can improve the acoustic noise reduction and uncover mechanical resonance frequencies in a total drive system. The digital random modulation strategies are implemented in drive systems based on PWM-VSI driven AC induction machines and give promising results. Similar implementation techniques are also used with a switched reluctance machine and tests show that random modulation strategies can be used with some benefits in order to reduce the acoustical noise emission