BRUSHLESS DC MOTOR CONTROL

The aim of this paper is to investigate controlling a Brushless DC Motor (BLDCM) using a Programmable Logic Controller (PLC) instead of micro controllers chips. As PLCs are now involved in most industrial processes, therefore, developing a program to handle the control of BLDCMs will save electronic components used in the drive circuit. Further, one PLC may control more than one motor via programming extra inputs and outputs already implemented in the PLC or simply by attaching additional input/ output cards. The speed is varied through the PWM technique. The PLC performed well with speeds up to 1550 rpm. The motor did not run faster due to the switching delay (scanning cycle time and hardware) of the PLC. Brushed DC motors have been used in industry due to their linear characteristics and the ease of adjusting their speed through a simple power electronic circuit. The commutator used in brushed DC motors is the main drawback for such systems which has motivated the researchers to direct their studies toward AC systems, induction and synchronous motors. Since the last decade, induction motors have dominated the industry due to the availability of the induction motors variable speed drives. However, these motors operate at low efficiency specially those of low power ratings. The solution for the drawbacks of brushed DC motors and AC motors can be found in BLDCMs, with superior performance. BLDCMs have similar characteristics to the separately excited DC machines but their control is similar to the AC machines control. This paper investigates the possibility of using a PLC (Programmable Logic controllers) to control such motors rather than microcontrollers Brushless DC motors can be divided into types, Sinusoidal BEMF and Trapezoidal BEMF. The present study deals with a BLDC motor with a trapezoidal BEMF BLDCMs’ BEMF has a trapezoidal wave form and the stator winding is fed by a rectangular current to produce constant torque. The three phase windings are placed on the stator and the rotor (with magnets) is free to move. There are always two phases on at any one time to provide continuous torque.