The operation stability of electrical drives with synchronous motors can be investigated by using models of small disturbance. The paper presents an analysis of operating stability for a synchronous motor fed by static frequency converter with current source inverter. On the basis of functional equations written in d-q system, based on the model of small variations, the operation stability are studied using the Routh-Hurwitz criterion. For a given angle of commutation, the synchronous motor is evaluated in different cases, with and without load, with and without damper windings. An instability is observed, when running the synchronous motor without damper windings, but also when assessing the leading angle variation relative to torque load variation.

Keywords: Synchronous motor, Current inverter, Stability