equivalent circuit of a separately-excited dc motor · connected to separately excited dc motor 35...

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Equivalent Circuit of a Separately-Excited

DC Motor

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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

3

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

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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

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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

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Equivalent circuit of a DC Series Motor

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( )

( )

( )

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

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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

Single phase semi-controlled converter fed

dc separately excited motor

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vOVm

0

iO

t

( )

t0

( )

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Speed-Torque Characteristics

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Single phase fully controlled converter fed

dc separately excited motor

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Speed-Torque Characteristics

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DC Series motor drive

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Single phase semi-controlled

converter fed dc series motor

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Speed-torque characteristics

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Single phase Fully controlled

converter fed dc series motor

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Speed-Torque Characteristics

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Three phase Half controlled converter

connected to separately excited DC motor

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ECE 442 Power Electronics 37

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ECE 442 Power Electronics 39

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Three phase fully controlled converter

connected to separately excited DC motor

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ECE 442 Power Electronics 42

Where VL is rms value line voltage

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Torque Speed Characteristic 44

DC series motor connected to 3 phase

half controlled bridge rectifier

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ECE 442 Power Electronics 47

Equivalent Circuit

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Speed torque characteristics

DC series motor connected to 3 phase

fully controlled bridge rectifier

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ECE 442 Power Electronics 50

Equivalent circuit under steady state

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Under steady state condition the following equations hold good

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Torque speed curves for different firing angles

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