The two-phase induction motor used as a servo motor

The performance of a 2-phase induction motor used as a servo motor depends upon the alteration of the machine from 2-phase to single-phase operation. This can be effected in three ways. Two depend upon change of applied voltage and the third depends upon alteration of the relative disposition of two stators in a specially constructed machine. The speed/torque relationship for the three conditions is deduced from the initial assumption that the flux-density distribution is sinu-soidal in space and time. The analysis reveals that single-phase motors have a maximum speed dependent upon the rotor resistance/reactance ratio as well as the frequency. It suggests a more appropriate definition of synchronous speed than that commonly accepted, namely as that speed at which the unidirectional torque becomes zero. Theoretical performance curves of the machine as a 2-phase motor, as a single-phase motor and in the intermediate condition between these two extremes are given, for various assumed resistance/reactance ratios, as a function of the parameter which alters the machine from 2-phase to single-phase operation. Comparison between theoretical and experimental curves is made. The resistance/reactance ratio of the 2-phase servo motor, required for effective speed control near zero speed, is demonstrated by the curves.