Elimination of increased excitation of common-mode oscillations in electrical drive systems with active front end and long motor cables

In this paper the analysis of common-mode oscillations in electrical drive systems is presented. The analysed oscillations occur especially in electrical drive systems with active front end, common DC link and long motor cables. Because of resonant frequencies at 10 to 40 kHz low damping occurs. Some motors with concentrated winding show resonant behaviour in this frequency range and increase the overvoltages from the terminals to the star point. For example a torquemotor is analysed and modelled. In the concerned frequency range switching operations generate a significant excitation. As the focus of this paper a special coupling mechanism is described. This mechanism enforces the excitation by the switching of the active front end. Afterwards remedies are analysed. Simulations and measurements on sample systems with and without remedies show apparent voltage stressing of motors, common-mode losses and currents that disturb the drive system.