Dynamics of a Four Quadrant Chopper Controlled D.C Machine at a Regulated Duty Cycle and Machine Speed for Efficient Drive Performance

摘要

Direct current (d.c) motors umpteen times are used in most adjustable speed drives and position controlled applications. They usually draw a very high armature current during starting which is usually higher than its rated value due to negligible back emf. This current value is often lethal to the commutator which conventionally should not have a current value greater than twice the rated value. To curb this hazardous effect of excess armature current, the d.c motor with separately excited d.c machine operation is regulated through a d.c armature voltage supply using a four quadrant duty cycle controlled chopper with variable d.c voltage output. This paper therefore explored the significances of attenuating the dangerous effect of high starting current on the commutator of the d.c machine using the voltage control method derived from duty cycle adjustment. Optimal drive performances with three different controlled closed loops were analyzed and achieved through simulation in MATLAB 7.11 to test for the machine speed responses and peak armature current values at duty cycles of 0.4, 0.6 and 0.8 respectively. Speed regulation values of -0.0018rad/Nm, -0.0491rad/Nm and -0.1159rad/Nm were obtained for the three closed loops. The control analysis showed that closed loop with a PI-controller gave the least transient and best steady state characteristics.