Overview Electrical Machines and Drives

1Challenge the future

Overview Electrical Machines and

Drives

• 7-9 1: Introduction, Maxwell’s equations, magnetic circuits

• 11-9 1.2-3: Magnetic circuits, Principles

• 14-9 3-4.2: Principles, DC machines

• 18-9 4.3-4.7: DC machines and drives

• 21-9 5.2-5.6: IM introduction, IM principles

• 25-9 Guest lecture Emile Brink

• 28-9 5.8-5.10: IM equivalent circuits and characteristics

• 2-10 5.13-6.3: IM drives, SM

• 5-10 6.4-6.13: SM, PMACM

• 12-10 6.14-8.3: PMACM, other machines

• 19-10: rest, questions

• 9-11: exam


DC machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• DC machine drives (4.5)

• Ward-Leonard system

• Power electronics (Rectifier, Chopper)

• Closed loop control

• PMDC machines / PCB machines (4.6, 4.7)


Ward-Leonard system

• dates from 1890

• is robust; can be overloaded

• is expensive and inefficient

Why does a diesel-electric locomotive have a comparable drive system?


Drive with power electronics


From DC source: chopper


From AC source: (controlled) rectifier


DC machines






• Ward-Leonard system

• Power electronics (Rectifier, Chopper)

• Closed loop control

• PMDC machines / PCB machines (4.6, 4.7)


Closed loop speed control


Closed-loop speed control with

inner current loop

• Why add an inner current loop?


DC machines






• PMDC machines (4.6, 4.7)

• iron armature

• hollow rotor

• disc armature


PM DC machine

Advantages:

• no field losses

• smaller machine

Disadvantages

• risk of demagnetisation

• no field control


Iron armature motor


Hollow rotor motor


Disc armature motor


DC machines






• PMDC machines (4.6, 4.7)



Drives








• 2-10 5.13-6.3: IM drives, SM

• 5-10 6.4-6.13: SM, PMACM



• 9-11: exam


Induction machines

• Introduction (5.1)

• Rotating magnetic field (5.2, also for SM)

• Why does an induction machine rotate?

• Induced voltage (5.3, also for SM)

• Definitions (5.4, 5.5)

• Equivalent circuits and voltage equations (5.7)

• Parameter identification (5.8)

• Performance characteristics (5.9)

• Power flow in three modes of operation (5.10)

• Speed control (5.13)

• Linear induction motors (5.16)


Introduction induction machines

• Why induction machines?

• cheap

• robust

• How are they used?

• motor

• generator in wind turbines

• How do they look?

• cylindrical rotor and stator bore

• laminated stator and rotor

• squirrel-cage rotor or wound rotor

• sinusoidally distributed stator winding


Three-phase induction machines

axes of the windingsthree phases


Cutaway view of an induction

machine


Three-phase stator winding


Three-phase stator winding


Squirrel cage rotor induction

machine


Wound rotor IM


Induction machines













Magnetic field of one phase

• one phase gives

pulsating

magnetic field


Assumptions

• Permeability of iron is infinite

• Stator winding is sinusoidally distributed

• Magnetic field crosses the air gap perpendicular

• Magnetic field in the air gap is not a function of the radius

• Magnetic field is symmetric: ( ) ( )B Bθ θ π= − +


Rotating magnetic field

NNNNa == ∫π

θθθθ0

21 d)(;sin)(Sinusoidally distributed winding:

( ) d 2m

m g g

C

F H s H lθ τ= ⋅ =∫� �

�Ampere’s law:

θθθθθθπθ

θ

πθ

θ

cosdsind)(d)( 21

aaaa

S

m NiNiNiAnJFm

===⋅= ∫∫∫∫++

��

0

( )( ) d 2

2m

mm g g g

gC

FF H s l H B

l

θθ τ µ= ⋅ = ⇒ =∫� �

�

Demo SMWithOnePhase Demo Rotating3Phase


Three pulsating fields

−−=−=

−−=−=

==

)cos()cos(ˆ)cos(),(



34

34

34

32

32

32

πωπθπθθπωπθπθθ

ωθθθ

tiNNitF

tiNNitF

tiNNitF

cmc

bmb

ama

−=−=

=

)sin()(

)sin()(

)sin()(

34

21

32

21

21

πθθπθθ

θθ

NN

NN

NN

c

b

a

−=

−=

=

)cos(ˆ)(

)cos(ˆ)(

)cos(ˆ)(

34

32

πωπω

ω

titi

titi

titi

c

b

a


One rotating field

2 23 3

4 43 3

ˆ( , ) cos( )cos( )

ˆ( , ) cos( )cos( )

ˆ( , ) cos( )cos( )

ma

mb

mc

F t Ni t

F t Ni t

F t Ni t

θ θ ωθ θ π ω πθ θ π ω π

= = − − = − −

−++−=

−++−=

++−=

)cos(ˆ)cos(ˆ),(

)cos(ˆ)cos(ˆ),(

)cos(ˆ)cos(ˆ),(

38

21

21

34

21

21

21

21

πωθωθθ

πωθωθθωθωθθ

tiNtiNtF

tiNtiNtF

tiNtiNtF

mc

mb

ma

)cos(ˆ),(),(),(),( 23 tiNtFtFtFtF mcmbmams ωθθθθθ −=++=

)cos(4

ˆ3),(

2),( 00 t

l

iNtF

ltB

gms

gs ωθµθµθ −==


Induction machines













Why does an IM work?

1 Sketch the flux linkage of dd’.

2 Sketch induced voltage in dd'.

The rotor turns dd’ and qq' are short-circuited via a large resistance Rr.

3 Sketch the current through dd'.

4 Sketch the flux density at the location of d’ B(π/2,t).

5 Sketch the flux density at the location of d' B(3π/2,t).

6 Sketch the torque on dd'.7 Sketch the torque on qq' in

the same way.

)cos(ˆ),( tBtBs ωθθ −=


Results


Conclusions

• constant torque with two turns

• at synchronous speed: no torque

• torque proportional to rotor frequency (slip frequency) if the

effect of the rotor currents on the field is negligible


Induction machines














Drives








• 2-10 5.13-6.3: IM drives, SM

• 5-10 6.4-6.13: SM, PMACM



• 9-11: exam

Documents

Overview Electrical Machines and Drives