This paper describes the design, construction, and
testing of a thyristorized speed control unit for a separately excited
dc motor. The motor is fed from a three-phase six-pulse fully contolled
thyristor bridge. A speed loop with a proportional plus integral
controller maintains the desired speed irrespective of the load variations
on the motor. An inner current control loop protects the
thyristors from overcurrents. This loop also provides fast response
overcoming the effect of disturbances such as variations in supply
voltage. The design aspects of the control loops are discussed, and
experimental results are given.