Damping Torsional Vibrations in Electrical Drives by SPWM Carrier-Shift Method

The paper analyses torsional vibrations in a 2-Degree-Of-Freedom (2-DOF) system caused by Sinusoidal Pulse-Width Modulation (SPWM) voltage harmonic. A relationship between the phases of the carrier signal and electromagnetic torque harmonic is presented. A method based on inverting the phase of the torque harmonic by imposing a periodic shift in the carrier signal is proposed. Consequently, the torsional vibrations excited by a specific shaft torque harmonic are significantly reduced. A criterion for choosing the appropriate phase shift is given, as well as for choosing the toggle time and the frequency range where the torque harmonic inversion takes place as long as the drive operates at/about mechanical resonance. The proposed method is validated by extensive laboratory tests on a 6.9 kW Permanent Magnet Synchronous Motor (PMSM) driving a dc machine. Both steady state and drive acceleration are tested.