Root locus application for damping capability estimation of multi-mass electromechanical systems

Special interest has been paid to the estimation of the damping capability of multi-mass electromechanical systems (EMS) and vibration suppression. Analysis and experiment results indicate that the maximal damping of two-mass systems depends on the mass ratio of the electric drive system. This paper uses the classical Evans root locus method to estimate the damping capability of the general multi-mass case. The root loci for three-mass systems are presented and cases which consider or neglect the electromagnetic time-constant are discussed. The critical values of the mass ratio are found. The cases of maximal damping and complete damping are determined. The influence of parameter variations is investigated by using multi-parameter root loci. Viscous friction on the motor shaft and on the load shaft is taken into account. It is shown that damping capability is more affected by variations in viscous friction on the load shaft than on the motor shaft. Numerical examples are provided for illustration