Torsional issues related to variable frequency control of elastic drive systems

Systems with variable frequency drives may experience torsional vibration. One reason is the pulsating nature of motor torque due to converter supply, another one is the electro-mechanical interaction and the effects of closed loop control. This paper deals with the speed control of elastic drive systems, mainly from torsional performance point of view. Modeling of elastic shaft string is being explored. The importance of control engineering to minimize the torsional vibration is explained. The paper also discusses different control strategies and their practical use in large resonant drive systems. Key factors in this part are complexity of the controller, its robustness and availability of required parameters. The practical aspects of the implementation in real control hardware are being considered. Attention is also paid to detection and monitoring of vibrations. Finally a verification method for correct parameterization on site is proposed. Different aspects are illustrated on simulations and calculations as well as on a real 6.1 MW compressor drive.