Techniques of PWM space vector modulation for the reduction of magnetic acoustic noise in traction motor

The aim of this work is the study and implementation of mixed random modulation techniques for the reduction of magnetic-acoustic noise in asynchronous motors for railway traction, fed by inverter. The current harmonics generated by PWM modulation cause an increase in the magnetic noise of the motor. The switching frequency is relatively low for this kind of application (typically 1-2 KHz) and it is included in the audible band. The use of random modulation techniques allows to distribute the higher tone energy all over the spectrum, getting a noise very similar to the background noise of a vehicle in motion. In this article new mixed PWM random modulation techniques are introduced, modifying both the pulse position and the PWM frequency. The results are better than the conventional techniques present in the literature. The proposed techniques have been tested on the propulsion system of Ansaldobreda Sirio Tram