Research on the effect of PWM Frequency on current of brushed DC motors

The dc motor is an attractive piece of equipment in many industrial applications requiring variable speed and torque characteristics due to its ease of controllability. Pulse Width Modulation (PWM) is a method of manipulating the DC voltage and current s duty cycle in which the rapid rising and falling edges of PWM signal minimises the switching transition time and the associated switching losses. In this paper the characteristics and performance of the brushed dc motor speed controller system was examined at different PWM frequencies using microcontroller. The main aim is to research the effect of PWM frequency on current and corresponding torque of motor. A PWM is generated using microcontroller ATmega16 which will drive the motor through a BJT transistor. L7805 and L7812 voltage regulators were used to supply 5V and 12V for the microcontroller and the motor drive circuits. The current was measured between the transistor source and ground. The simulation and experimental results show linear behavior with greater current at frequencies lower than calculated frequency at desired duty cycle and nonlinear behavior with lower current for frequencies higher than it.

Keywords:

DC motor , duty cycle , pulse width modulation , fast PWM , Microcontroller.