Dynamic Response of Voltage-Driven Induction Machines

Abstract

When operated at rated frequency, typical induction machines exhibit simple first or second order dynamic response depending upon machine size and load inertia and damping. At reduced frequency much more complex behavior can occur including the possiblity of small signal instability. This paper presents a general analysis of small signal dynamic behavior and introduces non-dimensional quantities which allow easy estimation of the region of poor dynamic response for specific machines. Graphical results which illustrate the regions of instability and poor damping are presented. The influence of machine parameters is described and the trends to be expected for different size and types of machines are discussed. In particular, 1t 1s shown that all machines pass through a minimum damping region as the frequency 1s reduced and that larger, more efficient machines will often exhibit small signal instability. An important result of the analysis is that all of the modifications made 1n producing “high efficiency machines” tend to produce more poorly damped behavior in the minimum damping region.