Chopper Fed Dc Motor
INTRODUCTION
During the nineteenth century, when power supply was dc, dc motors were used extensively to draw power direct from the dc source. The motor speed could be varied by adjusting field current by a rheostat. That was an open loop control. Most of the drives were constant speed and the characteristics could not be matched with a job requirement. A vast development in the dc drives system took place when the ward Leonard Control System was introduced in the 1980s. The system was motor-generator system to deliver power to the drive motor. The supply power available was still dc and dc motor was used to drive the dc generator set at a more or less constant speed. Afterwards when the ac power system came into existence and became popular, ac motors were developed and became attractive owing to their constructional simplicity, ruggedness and lower initial as well as maintenance cost. Machine requiring variable speed drives use the ward Leonard System employing ac motors driving dc motors at a constant speed. In the 1950s electronic came into existence and brought about remarkable improvement in the speed control system. The open- loop manual control system was replaced by close loop feedback control, which resulted in improved response and better accuracy. Initially, gas diodes and ignitrons were developed and ac to dc converters were used to control dc motors.
The advent of thyristors capable of handling large current has revolutionized the field of electric power control. Thyratrons, ignitrons, mercury arc rectifiers, magnetic amplifiers and motor generator sets have all been replaced by solid state circuits employing semi-conductor diodes and thyristors. Thyristor controlled drives employing both ac and dc motors find wide applications in industry as variable speed drives. In the 1960s ac power was converted into dc power for direct control of drive motors with solid state devices (high power silicon diodes and silicon
During the nineteenth century, when power supply was dc, dc motors were used extensively to draw power direct from the dc source. The motor speed could be varied by adjusting field current by a rheostat. That was an open loop control. Most of the drives were constant speed and the characteristics could not be matched with a job requirement. A vast development in the dc drives system took place when the ward Leonard Control System was introduced in the 1980s. The system was motor-generator system to deliver power to the drive motor. The supply power available was still dc and dc motor was used to drive the dc generator set at a more or less constant speed. Afterwards when the ac power system came into existence and became popular, ac motors were developed and became attractive owing to their constructional simplicity, ruggedness and lower initial as well as maintenance cost. Machine requiring variable speed drives use the ward Leonard System employing ac motors driving dc motors at a constant speed. In the 1950s electronic came into existence and brought about remarkable improvement in the speed control system. The open- loop manual control system was replaced by close loop feedback control, which resulted in improved response and better accuracy. Initially, gas diodes and ignitrons were developed and ac to dc converters were used to control dc motors.
The advent of thyristors capable of handling large current has revolutionized the field of electric power control. Thyratrons, ignitrons, mercury arc rectifiers, magnetic amplifiers and motor generator sets have all been replaced by solid state circuits employing semi-conductor diodes and thyristors. Thyristor controlled drives employing both ac and dc motors find wide applications in industry as variable speed drives. In the 1960s ac power was converted into dc power for direct control of drive motors with solid state devices (high power silicon diodes and silicon
Bibliography: 1. Electric Drives – Ramakrishnan, Prentice Hall India. 2. Power Electronics – P. S. Bimbhra, Khanna Publishers. 3. Software: MATLAB 6.5 and PSIM.