Newcastle Drives and Machines Group
Advances in Electric Machines: Topology, Materials and
Construction
Alan JackUniversity of Newcastle upon Tyne
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
What is new?The biggest by far is power electronicsPM,SRM,hybrids all possibleFrequency of choiceSpeed of choice
Silicon Carbide switching device
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
Dyson
100,000 rpm vacuum cleaner motor
Conventional 35,000 rpm universal motor stator
SR motor
Newcastle Drives and Machines Group
100,000 rpm appliance motor
Original motor 20,000 rpm
New motor
Newcastle Drives and Machines Group
Aeroengine fuel pump 16,000 rpm, 16 kW, runs fuel flooded
shear stress = 9.2 . 104 N/m2
Centrifugal stress = 5,800g
Newcastle Drives and Machines Group
Turbogenset high speed generator
Typical configuration30,000 rpm8 poles2kHz base frequencyTerminal volts 800 to 1,300 volts
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
Stator
Newcastle Drives and Machines Group
Magnets
Peak power 2.2MW
Peak force = 106 N
Newcastle Drives and Machines Group
Translator
Newcastle Drives and Machines Group
Enercon wind generator
4MW very slow = very big!
Newcastle Drives and Machines Group
Enercongenerator in the nacelle
Newcastle Drives and Machines Group
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?
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
Loadings
23Nm/kg
100 poles
Pf 0.41
Magnetic stress 5.52 . 105
very high! - bigger than the TG
& only naturally cooled
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
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?
Newcastle Drives and Machines Group
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?
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
Single Tooth Segment Approach to Machine Construction (Sheldon 1954)
Newcastle Drives and Machines Group
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
Newcastle Drives and Machines Group
Panasonic servo motors
Newcastle Drives and Machines Group
Yamada’s Patent of 1998
Newcastle Drives and Machines Group
Further Core Splitting Techniques
Mitsubishi Poki-Poki
Half lapped core back joints with clench pivot
Yaskowa separate tooth and core backs
Newcastle Drives and Machines Group
Slip on coils over the core back
Newcastle Drives and Machines Group
Mk 1
Newcastle Drives and Machines Group
Mk 2Shear stress = 1.4 . 104 N/m2
Centrifugal stress = 1227 g
Newcastle Drives and Machines Group
Little men laminations
Coil slips onto teeth
Newcastle Drives and Machines Group
Core wraps up - open circuit field
Newcastle Drives and Machines Group
All harmonicsincluding the even harmonics
spancoil,2
nsinn12F
n
=β⎟⎠⎞
⎜⎝⎛ β
π= ∑
•Losses in the magnet for PM
•Disaster for an IM!
Newcastle Drives and Machines Group
80mm frame size induction motor
Two stators displaced 180o wound backwards kills even harmonicsBut! zig-zag is very high
Newcastle Drives and Machines Group
Mk 2 non-overlapped with tooth splits
Newcastle Drives and Machines Group
No load with tooth splits
mag. Current increased slightly
Newcastle Drives and Machines Group
Rotor driven leakage flux
Still lots of zig-zag
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
Some Switched Reluctance stuff
SR’s are simple, rugged, motor is cheapButElectronics is more expensiveNoisyMotor is bigger than PM (but smaller then IM)
Newcastle Drives and Machines Group
What’s new in SR’s segmented rotorConventional 12/8 SR = 22.5Nm
Segmented 12/10 SR = 32Nm
PM 12/8 = 42Nm
Newcastle Drives and Machines Group
What’s new in SR’s 2: – flux switching - Black and Decker Circular saw motor
Newcastle Drives and Machines Group
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!
Newcastle Drives and Machines Group
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!