INDUCTION MOTOR SPEED CONTROL BY PULSE WIDTH MODULATION TECHNIQUE

INDUCTION  MOTOR  SPEED  CONTROL  BY  PULSE   WIDTH  MODULATION  TECHNIQUE

AIM:         

          The main aim of this project is to control the speed of induction motor  and here it is controlled by pulse width modulation technique

Description:

                There  are  many conventional  methods  of controlling  the  speed  of  an Induction motor. Among them V/F  control ,voltage control ,current control  are some of the methods. But here we are using PWM technique for controlling the speed of an induction motor. Pulse-width modulation (PWM) is a very efficient way of providing intermediate amounts of electrical power between fully on and fully off. A simple power switch with a typical power source provides full power only when switched on. PWM is a comparatively recent technique, made practical by modern electronic power switches .In the past, when only partial power was needed (such as for a sewing machine motor), a rheostat (located in the sewing machine's foot pedal) connected in series with the motor adjusted the amount of current flowing through the motor, but also wasted power as heat in the resistor element. It was an inefficient scheme, but tolerable because the total power was low. This was one of several methods of controlling power.

                         Here in this project we are implementing this pwm technique to the microcontroller for operation. basically it consists of  mainly a micro controller, optocoupler , triac , induction motor ,and increment and decrement switches. In electronics, an opto-coupler is a device that uses a short optical transmission path to transfer an electronic signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated—since the electrical signal is converted to a light beam, transferred, then converted back to an electrical signal, there is no need for electrical connection between the source and destination circuits. optocouplers change the state of their output when the input state changes; analog isolators produce an analog signal which reproduces the input. A TRIAC, or Triode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel  and with their gates connected together. The formal name for a TRIAC is bidirectional triode thyristor. This results in a bidirectional electronic switch which can conduct current in either direction when it is triggered (turned on) and thus doesn't have any polarity. It can be triggered by either a positive or a negative voltage being applied to its gate electrode . Here as said earlier there are two keys INC and DEC. by pressing these keys the speed can increased or decreased. These speeds can be controlled that is increased or decreased by controlling the firing angles.so by changing  the firing angles the speed is regulated through micro controller which is controlled through optocoupler which is further operated with triac and the whole is fed to the induction motor.thus we can obtain the control of  the induction motor.