SPEED CONTROL OF DC MOTOR USING PULSE WIDTH MODULATION

Submitted by :- Nidhi

Vijaywargiya Abhishikt

Animesh Vishwakarma

Content :•Introduction•D.C. motor

Working principle•Method of speed control

Pulse width modulation Circuit diagram & its description

•Advantages & Disadvantages•Application•Conclusion

Introduction :•Almost all the machine in industries operated

using electrical motors. Among them most of motors are DC motors.

•DC series motor is specially used for traction, electric locomotive, trolley systems, cranes and conveyor belt.

•All these works require frequent speed control for preparation of job.

•A PWM (Pulse Width Modulation) wave can be used to control the speed of the motor.

Working Principle:

•A machine that convert d.c power into mechanical power.

•It is based on electromagnetism i.e. when a current carrying conductor is placed in the magnetic field there is some mechanical force exerted on the current carrying conductor which is perpendicular to both the conductor and the magnetic filed.

•The most common DC motor types are the shunt wound and series wound types.

Speed control of dc motor :

•The purpose of a motor speed controller is to take a signal representing the required speed, and to drive a motor at that speed.

• Motor speed can be controlled by controlling- - Armature voltage (Va)- Armature current (Ia)

Cont………

•It is obvious that the speed can be controlled by varying

flux/pole, (Flux Control)

resistance Ra of armature circuit (Rheostatic Control)

applied voltage V (Voltage Control)

Cont…•The above methods have some demerits i.e

A large amount of power is wasted in the controller resistance. Hence, efficiency is decreased.

It needs expensive arrangement for dissipation of heat produced in the controller resistance.

It gives speeds below the normal speed.

Electronic Speed Control Methods for DC Motors :•compared to the electric and

electromechanical systems of speed control, the electronic methods have

higher accuracy

greater reliability

quick response

higher efficiency

Pulse Width Modulation :•Pulse width modulation (PWM) is a method for

binary signals generation, which has 2 signal periods (high and low).

•The width (W) of each pulse varies between 0 and the period (T).

•The duty cycle (D) of a signal is the ratio of pulse width to period.

•D=(t1+t2) / T

Pictures of the Waveform :

• The motor is on for most of the time and only off a short while, so the speed is near maximum

• The switch is on 50% and off 50%.

• The motor will only rotate slowly.

High Speed Signal (90%)

•The signal at the right shows the motor on for most of the time.

•The white dips indicate when the motor isn’t receiving power.

Signal With The Motor Half Speed (50%)

•The signal at the right shows the motor receiving power half the time.

Low Speed Signal (10%)

•The signal at the right shows the low speed signal which turns the motor slowly

Power Supply :

Circuit Description:•The transformer is a center tap 12-0-12V

500mA and supply 12v to the circuit.•The i/p sine wave is rectified by using full wave

rectifier which convert it to one constant polarity.

•A 1000Fcapacitor is used for filtration purpose.

•The three terminal voltage regulators 7812 provides regulated DC 12 v outputs for the operation of the circuit.

Advantage :

•PWM duty cycle control techniques enable greater efficiency of the DC motor .

•PWM switching control methods improve speed control and reduce the power losses in the system.

•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.

Disadvantages :

•The main Disadvantages of PWM circuits are the added complexity and the possibility of generating radio frequency interference .

•It can give speed below the full speed, not above.

•It cannot be used for fast controlling of speed.

Applications :•Traction application•Conveyor Belt carrying loads•Various motors requiring smooth speed

control•DC motors of all range can be controlled,

which are used for the production of materials•Electric locomotives•DC motor using precise job preparations

Conclusion

•The present project is practical one and high feasibility according to economic point of view, reliability & accuracy. It is programmable one therefore it can control various motors ranging small one to several hp motors.

Any query