The paper investigates the performance characteristics of a Solid-rotor induction motor when controlled using a 3-phase variable-voltage controller employing thyristors or triacs. In the method of analysis presented the output voltage waveform of the controller is analyzed using Fourier series and the motor equivalent circuits corresponding to different orders of harmonics are derived.

The current and torque characteristics of a 1 hp motor were computed using the approach presented. The computed results are compared with experimental results and good agreement was obtained.