The influence of the electromagnetic torque control loop on the dynamics of the two-mass drive system

In some industrial applications, such as rolling mill drives, torsional oscillations can occur due to the finite stiffness of the mechanical shaft. They degrade the performance of the drive system, can damage the mechanical part of the system, and in some cases they could lead to the control structure instability. One of the commonly used methods of damping torsional vibrations relies on the application of special control structures, i.e. the two control loops: electromagnetic torque and speed. During the design process of the speed loop the dynamics of the torque loop is very often neglected. This simplifies the synthesis of the speed controller and allows to shape the dynamics of the speed in a wide range. However, for fast dynamics of the speed control loop this assumption can lead to oscillations of the system state variables. In the paper an analysis of the twomass drive system with inertia caused by the torque loop and the state controller is carried out. The analytical formulas which allow to set the control structure parameter are provided. Selected simulation and experimental results confirm the theoretical considerations