Stepper-Motor and Switched- Reluctance Drives - Unicauca

Types: Variable Reluctance. Permanent Magnet ... Variable-reluctance stepper-motor designed to go into saturation ... Each pulse moves motor a discrete angle – step angle .... What is the equivalent-circuit representation of a stepper-motor?
Télécharger le PDF
104KB taille 106 téléchargements 482 vues
commentaire
Report
Chapter 14 Reluctance Drives: Stepper-Motor and SwitchedReluctance Drives

© 2000 http://www.ece.umn.edu/groups/electricdrives

Reluctance Drives Stepper – Motor and Switched – Reluctance Drives q Reluctance Drives • Stepper – Motor drives - Accurate position control without feedback - Electrical pulse input gives discrete angle change - Types: Variable Reluctance Permanent Magnet Hybrid • Switched – Reluctance drives - Variable-reluctance stepper-motor designed to go into saturation - Feedback necessary © 2000 http://www.ece.umn.edu/groups/electricdrives

14-1

14-2

Stepper-Motor Positioning qm

step angle

Electrical pulse input

l

0 0

t

t

q Each pulse moves motor a discrete angle – step angle q Counting pulses tells how far motor has turned without actually measuring (no feedback) © 2000 http://www.ece.umn.edu/groups/electricdrives

14-3

Reluctance Motors – Operating Principles l i (t )

+

fixed

q

RS T

l2 Dl

l1 e (t )

2

1 atq + Dq atq

-

0

q Salient rotor aligns to salient stator © 2000 http://www.ece.umn.edu/groups/electricdrives

i1

i

14-4

Stepper - Motors q Variable – reluctance motors - relies on rotor saliency q Permanent magnet motors - relies on rotor magnets q Hybrid motors - relies on both saliency and rotor magnets

© 2000 http://www.ece.umn.edu/groups/electricdrives

Variable – Reluctance Stepper Motors 1 q = rotor 3 tooth pitch

q =0 ia z

z

ib

2 q = rotor 3 tooth pitch

ia

q = 1 rotor tooth pitch

z

z

ic

© 2000 http://www.ece.umn.edu/groups/electricdrives

14-5

14-6

Variable - Reluctance Stepper Motors (cont…) q Rotor and stator saliency q Unequal number of poles q Stator current effectively pulls rotor pole in line with stator pole 3600 step-angle = qN r

© 2000 http://www.ece.umn.edu/groups/electricdrives

q = number of phases N r = number of rotor poles

14-7

Permanent Magnet Stepper Motor q = 0o

q = 45o A S N

A

B

N

S

z S

A S N

N

S

S N B

N

B z S N A

A N S

N S A S N

z

N

B

q = 135o

q = 90o

N

S B

S A

A

A

N S

A S N

N S A

q = 180o

zS N A

q Permanent magnets replace salient poles of variablereluctance motor © 2000 http://www.ece.umn.edu/groups/electricdrives

B N

S S

N z N S B N S B

14-8

Hybrid Stepper Motor L

R stator

S

windings

N shaft

S

end cap

N

end cap air gap

stator

outer casing

L'

R'

q Uses both rotor saliency and permanent magnets on rotor q Saliency on ends of rotor – ends not lined up q Permanent magnet makes one of the rotor ends a south pole and the other a north pole © 2000 http://www.ece.umn.edu/groups/electricdrives

14-9

Hybrid Stepper Motor (cont…) 8

1 N S

S

1 N

2

N

8

S

2

N

N

S

N

S

7S

S3

S

S

7S N

N S3

N

S N

N

6

S

S S N 5

4

N

N

6

1 8

N 1 S rotor 4 tooth pitch S

S 7

1 2

S

S

S

S

S N 6

4

N 5

S

S

S 5

© 2000 http://www.ece.umn.edu/groups/electricdrives

S4

8

S

N

N

N

N

2

N 3

7

N N

N

N N 6

N

N

N 5

S4

3

14-10

Stepper-Motor Equivalent Circuit i ph +

Rph L ph

v ph

-

© 2000 http://www.ece.umn.edu/groups/electricdrives

+ e ph -

14-11

Half–Stepping and Micro-Stepping ia

ib

q Possible to move rotor by half steps by exciting two stator windings equally q Finer steps possible by exciting two windings unequally © 2000 http://www.ece.umn.edu/groups/electricdrives

PPU for Variable-Reluctance Stepper-Motor +

v ph

+

-

T1 i ph

L ph

+

e ph

D1

-

Vd Phase winding D2

T2 Rsense

-

i ph

Iref

t

T1 on

T1 on

T1 off T2 on

© 2000 http://www.ece.umn.edu/groups/electricdrives

T1 ,T2 off

14-12

14-13

PPU for Variable-Reluctance Stepper-Motor (cont…)

q Currents do not need to reverse q Circuit uses “incomplete” switch poles that can pass current only one direction through the motor phase

© 2000 http://www.ece.umn.edu/groups/electricdrives

14-14

PPU for PM and Hybrid StepperMotor +

T1

D1

Phase winding

T3

D3

Vd D4

+

v ph

-

T4

T2

D2

-

q Phase currents must be reversible q Complete switch poles used © 2000 http://www.ece.umn.edu/groups/electricdrives

14-15

Switched-Reluctance Motor Drives ia

q = -30o

ia

q = 0o la

q = 0o

q = -30o ia

q q q q

Variable-reluctance stepper-motor Closed-loop, uses feedback Motor goes into saturation Rugged, inexpensive

© 2000 http://www.ece.umn.edu/groups/electricdrives

14-16

Summary/Review q What are the three broad categories of reluctance drives? q How is the principle on which reluctance drives operate different than that seen earlier with other drives? q Write down the reluctance torque expression. What does the direction of torque depend on? q Describe the operating principle of a variable-reluctance stepper-motor. q Describe the operating principle of a permanent-magnet steppermotor. q Describe the operating principle of a hybrid stepper-motor. q What is the equivalent-circuit representation of a stepper-motor? q How is half-stepping and micro-stepping achieved in steppermotors? © 2000 http://www.ece.umn.edu/groups/electricdrives

14-17

Summary/Review q What is the nature of power-processing units in stepper-motor drives? q Describe the operating principles of switched-reluctance drives. q What are the application areas of switched-reluctance drives?

© 2000 http://www.ece.umn.edu/groups/electricdrives