PWM Based Speed Control Of Ac Motor Using 8051 Controller
Published Thursday 6 October 2011 by gk inPWM Based Speed Control Of Ac Motor Using 8051 Controller
Project abstract:-
A PWM circuit works by making a square wave with a variable on-to-off ratio, the average on time may be varied from 0 to 100 percent. In this manner, a variable amount of power is transferred to the load. The main advantage of a PWM circuit over a resistive power controller is the efficiency, at a 50% level, the PWM will use about 50% of full power, almost all of which is transferred to the load, a resistive controller at 50% load power would consume about 71% of full power, 50% of the power goes to the load and the other 21% is wasted heating the series resistor. Load efficiency is almost always a critical factor in solar powered and other alternative energy systems.
One additional advantage of pulse width modulation is that the pulses reach the full supply voltage and will produce more torque in a motor by being able to overcome the internal motor resistances more easily. Finally, in a PWM circuit, common small potentiometers may be used to control a wide variety of loads whereas large and expensive high power variable resistors are needed for resistive controllers.
The project consists of a 4 x 2 keypad. This consist a total of 8 keys. The keys are connected to the Port 1 of Atmel at89c51 microcontroller. The microcontroller is programmed to scan for the key press, if it detects the key press. It automatically generates the pwm signals at a duty cycle, which is defined with respect to the key that was pressed. For example pressing the first key informs microcontroller to generate a pwm signal with duty cycle of 100% off. And pressing the second key will generate the pwm signal of 15 % ON time. And thus the seven keys makes motor to run with different level of duty cycle.
The generated pwm signals are taken from P2.0th pin of the microcontroller. The output is fed to the Optocoupler which has an inbuilt DIAC. The output of the optocoupler is fed to the gate pin of TRIAC. The triac drives the ac motor with respect to the triggering pulses that is obtained from the micro controller.
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