Digital Speed Control of a DC Motor With Phase-Locked Loop Regulation

This paper describes a digital speed control method of a rectifier-fed separately excited dc motor incorporating phase-locked loop technique. The converter uses cosine-wave crossing method, the digital version of which is generated by programming a set of read-only-memories (ROM). The smooth control of firing angle in the range of 0° to 180° permits motoring and regeneration in the full range, and four-quadrant operation is possible by reversing to motor field. A complete speed control system employing a 3/4-hp motor has been designed and tested in the laboratory and the experimental results agree wel1 with the theory. The principle can be easily extended to a three-phase system and higher horse power drives.