Advances in Electric Machines: Topology, Materials and ... · Newcastle Drives and Machines Group...

Newcastle Drives and Machines Group

Advances in Electric Machines: Topology, Materials and

Construction

Alan JackUniversity of Newcastle upon Tyne


There is nothing much in electrical machines which is truly new!

Alexanderson-Fessendeninductor alternator circa 1910

Looks a bit like a double sided TFM to me!


What is new?The biggest by far is power electronicsPM,SRM,hybrids all possibleFrequency of choiceSpeed of choice

Silicon Carbide switching device


What else in new? 1:

Hard magnetic materials – better performance lower price – leads to Increasing market penetrationA plethora of new geometriesA radical review of how machines are made


2: Soft magnetic materials

A steady advance in laminated steel propertiesSMC - soft magnetic composites, compacted insulated iron powder –hardly new Fritts patent came at the same time as Edison’s for laminations but now rapid advances in properties


00,20,40,60,8

11,21,41,61,8

0 2000 4000 6000 8000 10000 12000

H ( A/m)

B (

T)

Somaloy 500New SMC

SMC

10% lower saturationLow max permeability ~ 700High hysteresisLow eddy current

ButIsotropic propertiesNet shape with good tolerance and smooth surface finishNow starting to reach the market

20

30

40

50

60

70

80

Cor

e lo

ss (

W/k

g)Somaloy 500 Somaloy 550 NEW SMC

Material


3: Conductors and insulationNothing on the horizon for conventional conductors?Super conductors – rapid advances but still need very cold – defence applications now very much in the frame – commercial applications still limitedSteady advance in conventional polymersOxide systems making inroads combined with polymersCeramics close could lead to much higher temps


Let’s set some benchmarksTorque = 0.5 . Bn.Ht . Area. Radius

(sine wave assumption)

BnHt is a measure of the output/unit material

Bn air gap flux density limited by iron and/or magnets (except with super conductors) – 1T – less at v. high speedHt tangential magnetic field strength – limited by armature current heating – very flexible depends on cooling and arrangementTorque fixes the volume of the machine


Turbogenerators try very hard with cooling and speedTypical figures for hydrogen/water cooled Bn = 1THt = 3.105 A/m note: this is scale related for same cooling will fall as size reduces

Shear stress = 3.105

N/m2

Centrifugal stress = 8,000g

Drax 660MW- 2 pole

August 22nd 1966 – sweet 16 – those were the days!


The biggest bang for the buck1: how fast should we go?

50Hz is only right for 100’s of MW everything smaller should run at higher frequencyMotor size proportional to torque, power = torque x speed there is a good argument for faste.g. 30mm rotor (hand drill) for 8,300g means speed of 160,000rpm = times 8 on current power!


Dyson

100,000 rpm vacuum cleaner motor

Conventional 35,000 rpm universal motor stator

SR motor


100,000 rpm appliance motor

Original motor 20,000 rpm

New motor


Aeroengine fuel pump 16,000 rpm, 16 kW, runs fuel flooded

shear stress = 9.2 . 104 N/m2

Centrifugal stress = 5,800g


Turbogenset high speed generator

Typical configuration30,000 rpm8 poles2kHz base frequencyTerminal volts 800 to 1,300 volts


Lots of applications don’t want to go fast – lets drop the gearbox – direct drive…….

Archimedes Wave Swing

Electric Power Processing

TU Delft

This is going to hurt! Only 2.2MW from all that!


Stator


Magnets

Peak power 2.2MW

Peak force = 106 N


Translator


Enercon wind generator

4MW very slow = very big!


Enercongenerator in the nacelle


The biggest bang for the buck 2– can we do anything about the loadings

Bn = limited by steel (and magnets) to 1T1: drop the steel and the magnets, use superconductors – 4T now possible but it costs in £ and complexityThe military will (are) pay(ing)Can be economic at very large size >1000MW?


2: drop the steel and use loads of magnetsBn still 1T but big weight and volume reduction

Direct drive ironless wheel motor –Mecrow et al5Nm/kg naturally cooledLow inductance – keeps down converter VA – field weakening limited


3: Modulated pole machines –TFM, Claw Pole

All poles see all of the mmf –electric loading proportional to pole number

SMC Core Back

CoilMagnets

SMC RotoShaft & Hub

SMC Core Back

CoilMagnets

SMC RotoShaft & Hub

Claw Pole structure


Loadings

23Nm/kg

100 poles

Pf 0.41

Magnetic stress 5.52 . 105

very high! - bigger than the TG

& only naturally cooled


SMC Core Back

CoilMagnets

SMC RotorShaft & Hub

SMC Core Back

CoilMagnets

SMC RotorShaft & Hub

Claw Pole structure

An interjection:The design issue

Convoluted magnetic circuit plus high electric loading = very high reactance with lots of leakageThe key to good design is to maximise the magnetic flux whilst minimising the armature fluxMost of the armature flux is leakage fluxGet the leakage down


It leaks all over the place!

Upper portion

Lower portion

Magnets

Tooth tips

Rotor

SL INT 2

SL INT 1

SL A/G

View DirectionAxial

Magnets

Air

View Direction Radial towards axis of rotation SL END

Rend

SL3 SL2

rL

xs

Air gap leakage Flux, SL1

SL4

SL5


Res

ulta

nt F

lux

= 74

.6 m

Wb

W

indi

ng so

urce

1.4 91

14

5.0

5.00.04

0.04

0.7

0.7 1.2

1.2 14

14

14

14

141

357

57

141

357

Mag

net s

ourc

e

Tooth/core backS1, S2, S3 & S4

Air gap Sgap

Magnet Smag

14

60

136

43.5

7.6

3.3

4.2 21.5

41.2

31.1

64.5

85.8

80.1

48.1

31.7

0.6

5.7

15.6

16.4

16.4

2.3 0.9

3.3

13.9

19.8


Lumped circuit + GA made this design - 1.1 £/Nm

But we realised this would be better 0.94 £/Nm 7.3Nm/kg active

Unsolved problem 1: how do you tell the optimiser to use its imagination?


The only way forward seemed to be optimisation with 3D FE in the loopWe need to get the leakage flux right needs 3DWe are having difficulty imagining the field – can the optimiser tell us what is going on?The answer is not very well!What does optimum mean anyway?


PM machines – “new” freedomsModern PM’s very powerful – extreme example TG makes 0.5.106 ampturns would need 400mm magnet depth – would fit!Magnet strength prop depth winding strength with area at small sizes magnet has massive advantageMagnets don’t conduct (much!)Magnets are not permeableMagnets have fixed pole numberCan take terrible liberties with magnetic and electric circuit!


Explosion in methods of construction - Its all about non-overlapped coils

Non-overlapped coils let you tear the motor apartMake the end windings shorterAllow slots to be fully filled even with full automation


Single Tooth Segment Approach to Machine Construction (Sheldon 1954)


Overlapped coils ->= 1 slot/pole/phasepitch, distribution, sine waves25-40% slot fillmanual or complicated winding machines

Non-overlapped -0.25 to 0.5 slots/pole/phase - harmonics

60-80% slot fillbobbin winding - simple - flexible


Panasonic servo motors


Yamada’s Patent of 1998


Further Core Splitting Techniques

Mitsubishi Poki-Poki

Half lapped core back joints with clench pivot

Yaskowa separate tooth and core backs


Slip on coils over the core back


Mk 1


Mk 2Shear stress = 1.4 . 104 N/m2

Centrifugal stress = 1227 g


Little men laminations

Coil slips onto teeth


Core wraps up - open circuit field


All harmonicsincluding the even harmonics

spancoil,2

nsinn12F

n

=β⎟⎠⎞

⎜⎝⎛ β

π= ∑

•Losses in the magnet for PM

•Disaster for an IM!


80mm frame size induction motor

Two stators displaced 180o wound backwards kills even harmonicsBut! zig-zag is very high


Mk 2 non-overlapped with tooth splits


No load with tooth splits

mag. Current increased slightly


Rotor driven leakage flux

Still lots of zig-zag


0

2

4

6

8

0 500 1000 1500rpm

Torq

ue (N

m)

ConventionalMK 1 non-overlappedMk 2 non-overlapped

Torque-slip curvesStill some work to do!


Some Switched Reluctance stuff

SR’s are simple, rugged, motor is cheapButElectronics is more expensiveNoisyMotor is bigger than PM (but smaller then IM)


What’s new in SR’s segmented rotorConventional 12/8 SR = 22.5Nm

Segmented 12/10 SR = 32Nm

PM 12/8 = 42Nm


What’s new in SR’s 2: – flux switching - Black and Decker Circular saw motor


What’s the best cheap motor?

The commutator machine is still the cheapest fixed or variable speed drive!150 motors in Mercedes S class all bar one brushed DCMost domestic products driven by Universal motorIt’s the cost of the electronics!


To Conclude:If electronics cost next to nothing (big if!!!):IM looses all roundSRM might win somePM wins (if magnets keep falling in price!)

The biggest motor challenge bar none is to get the cost of the electronics downBut - lots more fun to be had with machines!

Advances in Electric Machines: Topology, Materials and ... · Newcastle Drives and Machines Group...

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