Development and study of a microprocessor-based direct current motor controller

Abstract

Control systems for electric motors have become so vital to the proper performance and protection of modern plant equipment that they are frequently the most essential links in complex industrial applications. Electric motors play a very important part in furnishing power for all types of domestic and industrial applications. Understanding the direct current drive is particularly important because it is so widely used as a yardstick by which other drives are measured. Users who develop a good grasp of the direct current drive will find their knowhow invaluable in dealing with all other types, particularly if they can establish a firm grip on the philosophy of the control scheme. Analogue and digital motor control systems already exist. These control systems have inherent weaknesses such as lack of system's flexibility, poor responses, large power losses, several switches and relays, large complexity of wiring, and a large number of circuitry. This thesis presents a control system based on a 8088 microprocessor for starting, stopping and changing the direction of DC motors. The hardware consists of the micro-controller and the switching circuit connected to the motor. The microprocessor with the help of a clock produces pulses which are output through the port B of the Programmable Peripheral Interface (8255). This signal was fed to the switching circuit through a non inverting buffer. To run a motor both forward and reverse, an H-bridge circuit has been set that can reverse its polarity. The average voltage applied to the motor depends on the amount of time when the switch is ON with respect to the time when the switch is OFF (duty cycle). The control software was developed using assembly language and coded in 8086/8088 assembler. Experimental results were achieved using Light Emitting Diodes (LEDs) and a PM 3384 Autoranging Combiscope. The system possesses some advantages over the analog and digital motor controllers.