SPEED CONTROL OF DC MOTOR USING PULSE WIDTH MODULATION : SPEED CONTROL OF DC MOTOR USING PULSE WIDTH MODULATION Submitted by
SHAKTI MOHAN PATNAIK(06-3261)
RITESH KUMAR LENKA(06-3262)
EIE, 7th SEM
Under Guidance of
Mr. Rakesh Kumar Patnaik Content : : Content : Introduction
Types of motor
Method of speed control
Pulse width modulation
Circuit diagram & its description
Advantages & Disadvantages
Conclusion Introduction : : 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: : 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. Shunt wound motor : : Shunt wound motor : Shunt wound motor are used for driving constant speed shafts, centrifugal pumps, blower & pumps etc.
The characteristics of a DC shunt wound motor give it very good speed regulation, and it is classified as a constant speed motor, even though the speed does slightly decrease as load is increased.
Shunt-wound motors are used in industrial and automotive applications where precise control of speed and torque are required. Series wound motor : : Series wound motor : The advantage of a Series Wound Motor is that it develops a large torque and can be operated at low speed.
It is a motor that is well-suited for starting heavy loads; it is often used for industrial cranes and winches where very heavy loads must be moved slowly and lighter loads moved more rapidly.
DC series motor is specially used for traction, electric locomotive, trolley systems, cranes hoists and conveyor Speed control of dc motor : : 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
Armature voltage (Va)
Armature current (Ia) Cont……… : 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… : 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 : : Electronic Speed Control Methods for DC Motors : compared to the electric and electromechanical systems of speed control, the electronic methods have
higher efficiency Principle : : Principle : The main principle is control of power by varying the duty cycle.
Here the conduction time to the load is controlled.
for a time t1, the input voltage appears across the load ie
for t2 time the voltage across the load is zero.
The average voltage at output is given by
Va = 1/T vodt = t1/T Vs = ft1 Vs = kVs
the average load current
Ia = Va/R = KVs/R
where T is the total time period =t1+t2
k = t1/T is the duty cycle Cont…… : Cont…… The rms value of output voltage is
V0 = ( i/T V02 dt ) ½ = k Vs
The output power and is given by
Pi = 1/T v0idt = 1/T v02/R dt = kVs2/R
The duty cycle can be varied from 0 to 1 by varying t1, T or f. Therefore, the output voltage V0 can be varied from 0 to Vs by controlling k, and the power flow can be controlled.
As the time t1 changes the width of pulse is varied and this type of control is called pulse width modulation (PWM) control. Pulse Width Modulation : : 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 : : 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%) : 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%) : Signal With The Motor Half Speed (50%) The signal at the right shows the motor receiving power half the time. Low Speed Signal (10%) : Low Speed Signal (10%) The signal at the right shows the low speed signal which turns the motor slowly Circuit Description : : Circuit Description : Power supply
Motor Controller Power Supply : : Power Supply : Circuit Description: : 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. Circuit Diagram : (Motor Controller Sections) : Circuit Diagram : (Motor Controller Sections) Circuit Description : : Circuit Description : The design is based on astable multivibrator IC1a.
output is low for a period determined by R1 and high for a period set by R2 and P1.
When C1 is discharged, the level at the input of IC1a is below the lower threshold, so that the output of this stage is high.
The capacitor is then charged rapidly via D1 and R1, and reaches the upper threshold in about
t = ln(2)RC
=1.5 ms Cont….. : Cont….. As output of IC1a goes low, whereupon C1 is discharged via D2, R2, and P1.
The discharge time could be set between 0.2ms and 25ms.
the duty factor of the output signal may be varied between 5% and 90%.
The signal is inverted again and then applied to the input of transistor BC557 through 4k7.
The transistor Bc557 act as a buffer which transfer electrical impedance from one circuit to another circuit i.e. it act as a pre amplifier. Cont… : Cont… The o/p of Bc557 is given to the power transistor 2N3055 which is used in a circuit as an amplifier, detector, or switch.
The diode connected across the motor is for freewheeling purpose i.e. the diode used to eliminate flyback, the sudden voltage spike seen across an inductive load when its supply voltage is suddenly reduced or removed.
The resistance of P1(Potentiometer) is at a minimum, the rotary speed of the motor is at a maximum. Advantage : : 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 : : 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 : : 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
DC motor using precise job preparations Conclusion : 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 : Any query