CONSTANT TORQUE CLOSED-LOOP ROTOR RESISTANCE CONTROLLER FOR DC DYNAMIC BRAKING OF A WOUND ROTOR INDUCTION-MOTOR

A closed loop rotor resistance controller using a thyristor chopper in the rotor circuit for improving the DC dynamic braking performance of a wound rotor induction motor is presented. The control of rotor resi stance is achieved by varying the duty cycle of the chopper from zero to almost unity based on the magnitude of the rotor current. During br aking the feedback controller maintains a constant rotor current which results in reduced stopping time and minimum heat dissipation. The un ique design of the controller allows torque control even at low speeds without the need for an auxiliary power supply for forced commutation of the controller's thyristors.