Stability Analysis of a Symmetrical Induction Machine

A stability study of an induction machine is performed by applying the root-locus criterion to the equations which describe the behavior of the machine during small displacements about a steady-state operating point. This investigation reveals that a symmetrical induction machine may become unstable at low speeds (low frequencies) even though balanced, constant amplitude, sinusoidal voltages are applied to the stator terminals. Regions of machine instability are established from the results of a digital computer study. The results of an analog computer study are included to illustrate the modes of operation which occur within these regions. Regions of instability for changes of system parameters are presented and discussed. Also, it is shown that the root- locus criterion can be utilized to identify regions of lightly damped operation.