An Experimental Closed-Loop Variable Speed Drive Incorporating a Thyristor Driven Induction Motor

Closed-loop control of a 3-phase induction motor is investigated where the stator voltages are varied, at line frequency, by the controlled firing of silicon-controlled rectifiers (thyristors). Steady-state torque-speed curves are given and the transient response of the drive to step changes of reference signal is shown. The rapid transient response of the drive due to transistorized thyristor firing circuits is demonstrated. The transfer function of the thyristor power modulator cannot be specified independently of the transfer function of the motor.