DC DRIVE 1

Controlled-Rectifier Fed Drive

Armature Field

Dc drive 2

Chopper-Fed Drive

Armature Field

Dc drive 3

Equivalent Circuit of a Separately-Excited

DC Motor

Dc drives 4

f

f f f f

aa a a a g

g v f

d t f a

d L

div R i L

dt

div R i L e

dt

e K i

T K i i

dT J B T

dt

Dc drive 5

0

f f f

g v f

a a a g

a a a v f

d t f a

d L

d d

Steady state

d

dt

V R I

E K I

V R I E

V R I K I

T K I I

T B T

P T

Dc drive 6

a a a v f

a a a a a a

v f f

v

f

V R I K I

V I R V I R

K I VK

R

Solve for the motor speed

Dc drive 7

Control of the motor speed

• Control armature

voltage, Va

– Voltage control

• Control the field

current, If– Current control

• Control the armature

current, Ia

a a a

f

v

f

V I R

VK

R

Dc drive 8

Magnetization Characteristic

Dc drive 9

Characteristics of Separately-Excited Motors

Rated

speed

Use field-current control

Use armature

voltage control

Dc drive 10

Equivalent circuit of a DC Series Motor

Dc drive 11

( )

( )

( )

g v a

a a f a g

a a f a v f

d t a f

d L

a a f a

v f

E K I

V R R I E

V R R I K I

T K I I

T B T

V R R I

K I

Dc drive 12

Controlling the Motor Speed

• Control the armature

voltage, Va

• Control the armature

current, Ia

( )

( )

( )

g v a

a a f a g

a a f a v f

d t a f

d L

a a f a

v f

E K I

V R R I E

V R R I K I

T K I I

T B T

V R R I

K I

Dc drive 13

Characteristics of DC Series motors

Dc drive 14

Operating Modes

• In variable-speed applications, a dc motor

may be operating in one or more of the

following “Modes”

• Motoring

• Regenerative braking

• Dynamic braking

• Plugging

Dc drive 15

Motoring Mode

“Back emf”, Eg is < supply voltage Va

Both Ia and If are positive

Developed torque meets load demand

Dc drive 16

Regenerative Braking Mode

Motor acts as a Generator

Eg becomes > supply Voltage Va

Ia becomes negative

Kinetic energy of the motor is returned to the supply

Dc drive 17

Dynamic Braking

Replace the supply voltage with a resistor

Power dissipated in the resistor rather than given back

to the source

Dc drive 18

Plugging

Reverse the armature terminals while running

Va and Eg act in the same direction

Ia is reversed, producing “braking” torque

ECE 442 Power Electronics 19

Four-Quadrant Operation

Dc drive 20

Single-Phase DC Drive

Change Va by changing firing angle

Inductor Lm is a “smoothing” Inductor to prevent

discontinuous current

Dc drive 21

Armature Reversal

Dc drive 22

Field Reversal

Dc drive 23

Single-Phase Half-Wave Converter Drive

(1 cos )2

0

(1 cos )

0

ma a

a

mf f

f

VV

VV

Dc drive 24

Quadrant of Operation

Dc drive 25

Waveform Summary

Dc drive 26

Single-Phase Semiconverter Drives

(1 cos )

0

(1 cos )

0

ma a

a

mf f

f

VV

VV

Dc drive 27

Quadrant(s) of Operation

Semiconverter – one quadrant converter

One polarity of output voltage and current

Dc drive 28

Waveform Summary

Dc drive 29

Single-Phase Full-Converter Drives

Dc drive 30

Quadrant(s) of Operation

Full converter – two quadrant converter

Output voltage polarity can be positive or negative

Output current has one polarity

Dc drive 31

Waveform Summary

Dc drive 32

Single-Phase Dual-Converter Drives

Dual converter can operate in all four quadrants

Output voltage and current can be positive or negative