Commutation by armature induced voltage in self-controlled synchronous machines

Abstract

A self-controlled synchronous machine drive system consists of a frequency converter, a control loop utilizing a shaft angle sensor as the primary control input, and a conventional synchronous machine. The static and dynamic characteristics of the system are similar to those of a dc machine. In a drive system of this type, the commutation of current between phases of the synchronous motor is the factor which ultimately limits the peak torque that the system can develop. In this paper a system model valid during the commutation interval is formulated using direct phase variables. The resulting equations with time varying coefficients are put into state variable form and are solved using conventional step by step numerical integration procedures. Results show that proper choice of damper winding parameters can significantly reduce commutation time while simultaneously increasing the maximum current that can be successfully commutated. In general, damper winding resistances are shown to have little effect on commutation limits whereas low values of damper and stator winding leakage reactance are necessary to insure commutation over a large load range. Since earlier work on drive systems of this type has shown that damper windings are not essential for system stability, the damper winding design should be guided by consideration of optimum commutation performance. Copyright © 1974 by The Institute of Electrical and Electronics Engineers, Inc.