Torsional vibration in large variable speed drive systems: Origin and mitigation methods

Drive systems incorporating variable speed drives (VSD) may experience torsional vibration. The root cause is often explained as torque pulsations produced by the drive. In fact, the vibration phenomenon can typically appear from two reasons: Excitation of torsional resonance by torque ripple, and closed loop electro-mechanical interaction between VSD and driven load. This paper aims to provide a comprehensive analysis on the origin of such vibrations and to propose control modifications to increase the damping and mitigate torsional vibration issues. Time-domain simulations and frequency-domain analysis are used to parameterize the converter control properly. For load-commutated inverters (LCI) a robust active damping function is presented. Passive damping in the speed control loop suitable for any type of variable speed drive is described as well.