Control of DC DrivesBY: Keval Patel(100110111007)

Sandip Dobariya(100110111013)

Introduction:

The most common form of variable speed D.C. driveis based on the control of armature voltage.

The speed of D.C. motor has to be controlled froman A.C. or D.C. source.

More commonly controlled rectifier is used to supplythe motor armature.

Phase locked loop control techniques are employed insome D.C. Drives to provide the precise speedcontrol.

Types of configuration:

Series exited D.C. motors:

Series motors are traditionally employed for traction application.

Separately exited D.C. motors:

At present, separately exited D.C. motors controlled by thyristor

convertors are the most widely used motor drive system in industry.

D.C. drives

Single phase drives

Three phase drives

Chopper drives

Single phase and three phase D.C.

drives:

The converter used for particular application depends on

such factors as supply available one phase or three phase.

D.C. chopper drives:

To control the speed of DC motors, we can control the motor

terminal voltages. The chopper output voltage is proportional

to the chopper switching frequency and its duty cycle, so the

magnitude of voltages entering the terminal motors can be

adjusted, and so the motor speed.

Control of D.C. motor’s speed by a chopper is required where

the supply is D.C. (as from a battery) or an A.C. voltage that

has already been rectified to a D.C. voltage.

The most important application of choppers are in the speed

control of D.C. motors used in industrial or traction drives.

D.C. chopper drives:

Choppers are used for the control of D.C. motors because

of number of advantages, such as high efficiency,

flexibility in control, light weight, small size, quick

response.

Chopper control D.C. drive has also application in servos

in battery operated vehicles such as forkflift, trolleys so

on.

PLL control of D.C. drives:

In the phase-locked loop method, motor speed is

converted to a digital pulse train, which is synchronized

with a reference digital pulse train. In this way, by locking

onto a reference frequency, precise control of motor

speed is achieved.

PLL control of D.C. drives:

Phase detector

LPF ConverterD.C.

motors

Speed encoder

fi

f0

Ee Ec Eaw

Advantages:

Smaller in size

Very efficient

Highly reliable

Applications:

1. Rolling mills

2. Paper mills

3. Printing press

4. Mine winders

5. Machine tools

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