Speed Control of Direct Current Motors
Authors: Onah AJ, Awah CC, Diyoke GC
DOI Info: http://doi.org/10.5281/zenodo.6726399
Direct current (DC) motors are used in variable-speed drives to produce a high starting torque, and provide speed control over a wide range of speed. Controlled rectifiers are popularly employed in the speed control of DC motors. In this paper, the speed control of separately excited dc motor, using single-phase, full-wave, fully-controlled rectifier was investigated. Controlled rectifiers were used to produce variable DC output voltages from a fixed alternating current (AC) voltage. Since the armature voltage (Va) of a DC motor is the output of a single-phase controlled rectifier, it was varied by varying the delay or firing angle (?a) of the rectifier. The field circuit also requires a rectifier to control the field current (If) or flux by varying the firing angle (?f). In this paper, the motor speed equations were derived. The output equations of the rectifiers were also derived and incorporated into the motor speed equations. The graphs generated from these equations show clearly how the speed of the DC motor varies with the output voltage or current of the controlled rectifiers. Thus, motor speed, being a function of the armature voltage (Va), or the field current (If) was controlled. This paper demonstrates the control strategies of a separately excited dc motor, using single-phase controlled rectifiers.
Affiliations: Department of Electrical/Electronic Engineering, College of Engineering and Engineering Technology, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria.
Keywords: DC Motors, Variable-speed Drives, Fully-controlled Rectifier, Delay-angle, Torque, Armature-voltage Control, Field Control
Published date: 2022/06/30