Design and implementation of a three phase thyristor phase controlled rectifier for a DC Motor

Abstract

Variable speed control is a requirement found amongst various industrial high power DC motors. The three phase thyristor phase controlled AC/DC converter is a popular choice for DC motor adjustable speed drives (ASD). Phase angle control permits the adjustment of the DC average output voltage of the converter applied across the armature of the motor. This dissertation is concerned with the design and implementation of a six-pulse bridge rectifier to be used as a variable speed drive (VSD) for a separately excited DC motor. The main features within the design include; input supply AC voltage synchronization, design of a real time control firmware, thyristor gate triggering and a user interface. The converter demonstrated to work as expected and all elements within the system proved to be working correctly. The converter output DC voltage showed that the thyristors are being activated at accurate firing times. Adjusting the firing angle by means of the designed controller brought about a change in the output average voltage, thus regulating the speed of the motor.