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1

Electric Drives

Chapter 7 – DC-motor drives and

electronically-commutated motor

drives

TET4120 Electric Drives

2

Cost comparison

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3

DC drives – structure and

classification

4

Mechanical structure

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5

Rotors with armature winding and

commutator 

6

Flux density in airgap

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7

8

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DC machine torque and emf 

T E 

mE mf 

a

mf 

a

a

aT af 

aa

f aem

k k 

k lrBn

r l Bn

e

i k i lrBn

lr i 

BnT 

 

  

 

 

  

 

 

  

 

 

  

 

   22

22

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11

 Armature reaction

12

DC machine equivalent circuit

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13

DC motor drives operating

modes

14

Four-quadrant operation

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Flux-weakening in wound field

machines

rated m

m

,

 

 

rated em

em

T 

T 

,

16

Electronically-Commutated(Brushless DC) Motor drives

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18

6012060

9022

1201202

1206060

9022

60602

    

 

   

    

 

   

for lr BN 

for lr BN 

for lr BN 

for lr BN 

e

mf s

mf s

mf s

mf s

a

Induced emf 

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19

Torque

production

• Force on conductors: f = Bli

• Torque on conductors: T = fr 

• Current in two windings at atime. Total torque:

Tem = 2(2NsBf lr)i = kTi

20

Current and torque ripple