Effects of PWM techniques on common mode currents in induction motor drives

Common mode currents have been experienced on last generation drives causing damages on ball bearings and the generation of electromagnetic emissions. Such currents, generated by fast variations of common mode voltage, must be suitably limited in order to improve the reliability of modern drives and to reduce electromagnetic emissions. This is normally achieved by means of low pass filters, but at the cost of increased costs and sizes. An alternative inexpensive approach consists in using specifically designed modulation strategies. In the paper a new digital PWM modulation strategy is introduced able to reduce common mode currents by limiting the amount of common mode voltage variations. An experimental evaluation of the proposed strategy on an induction motor drive is provided in order to demonstrate the consistency of the new approach.