Advances in Electric Machines: Topology, Materials and Construction. Alan Jack

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1 Advances in Electric Machines: Topology, Materials and Construction Alan Jack University of Newcastle upon Tyne

2 There is nothing much in electrical machines which is truly new! Alexanderson -Fessenden inductor alternator circa 1910 Looks a bit like a double sided TFM to me!

3 What is new? The biggest by far is power electronics PM,SRM,hybrids all possible Frequency of choice Speed of choice Silicon Carbide switching device

4 What else in new? 1: Hard magnetic materials better performance lower price leads to Increasing market penetration A plethora of new geometries A radical review of how machines are made

5 2: Soft magnetic materials A steady advance in laminated steel properties SMC - 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

SMC 10% lower saturation Low max permeability ~ 700 High hysteresis Low eddy current But Isotropic properties Net shape with good tolerance and smooth surface finish Now starting to reach the

6 SMC 10% lower saturation Low max permeability ~ 700 High hysteresis Low eddy current But Isotropic properties Net shape with good tolerance and smooth surface finish Now starting to reach the market B (T) 1,8 1,6 1,4 1,2 1 0,8 Somaloy 500 0,6 New SMC 0,4 0, H ( A/m) 80 C ore loss (W/kg) Somaloy 500 Somaloy 550 NEW SMC Material

7 3: Conductors and insulation Nothing 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 limited Steady advance in conventional polymers Oxide systems making inroads combined with polymers Ceramics close could lead to much higher temps

8 Let s set some benchmarks Torque = 0.5. B n.h t. Area. Radius (sine wave assumption) B n H t is a measure of the output/unit material B n air gap flux density limited by iron and/or magnets (except with super conductors) 1T less at v. high speed H t tangential magnetic field strength limited by armature current heating very flexible depends on cooling and arrangement Torque fixes the volume of the machine

Turbogenerators try very hard with cooling and speed Typical figures for hydrogen/water cooled B n = 1T H t = 3.

9 Turbogenerators try very hard with cooling and speed Typical figures for hydrogen/water cooled B n = 1T H t = A/m note: this is scale related for same cooling will fall as size reduces Shear stress = N/m 2 Drax 660MW- 2 pole August 22 nd 1966 sweet 16 those were the days! Centrifugal stress = 8,000g

10 The biggest bang for the buck 1: how fast should we go? 50Hz is only right for 100 s of MW everything smaller should run at higher frequency Motor size proportional to torque, power = torque x speed there is a good argument for fast e.g. 30mm rotor (hand drill) for 8,300g means speed of 160,000rpm = times 8 on current power!

11 Conventional 35,000 rpm universal motor stator Dyson 100,000 rpm vacuum cleaner motor SR motor

12 100,000 rpm appliance motor Original motor 20,000 rpm New motor

13 Aeroengine fuel pump 16,000 rpm, 16 kw, runs fuel flooded shear stress = N/m 2 Centrifugal stress = 5,800g

14 Turbogenset high speed generator Typical configuration 30,000 rpm 8 poles 2kHz base frequency Terminal volts 800 to 1,300 volts

15 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!

16 Stator

17 Magnets Peak power 2.2MW Peak force = 10 6 N

18 Translator

19 Enercon wind generator 4MW very slow = very big!

20 Enercon generator in the nacelle

21 The biggest bang for the buck 2 can we do anything about the loadings B n = limited by steel (and magnets) to 1T 1: drop the steel and the magnets, use superconductors 4T now possible but it costs in and complexity The military will (are) pay(ing) Can be economic at very large size >1000MW?

22 2: drop the steel and use loads of magnets B n still 1T but big weight and volume reduction Direct drive ironless wheel motor Mecrow et al 5Nm/kg naturally cooled Low inductance keeps down converter VA field weakening limited

23 3: Modulated pole machines TFM, Claw Pole All poles see all of the mmf electric loading proportional to pole number SMC Core Back Coil Magnets Claw Pole structure SMC Roto Shaft & Hub

Loadings 23Nm/kg 100 poles Pf 0.41 Magnetic stress 5.52.

24 Loadings 23Nm/kg 100 poles Pf 0.41 Magnetic stress very high! - bigger than the TG & only naturally cooled

25 Claw Pole structure SMC Core Back Coil Magnets An interjection: The design issue SMC Rotor Shaft & Hub Convoluted magnetic circuit plus high electric loading = very high reactance with lots of leakage The key to good design is to maximise the magnetic flux whilst minimising the armature flux Most of the armature flux is leakage flux Get the leakage down

26 It leaks all over the place! Tooth tips S L A/G View Direction Axial Air S L END View Direction Radial towards axis of rotation R end Magnets S L INT 2 Upper portion S L INT 1 Lower portion Rotor Magnets Air gap leakage Flux, S L1 S L5 rl x s S L4 S L2 S L3

27 Winding source Resultant Flux = 74.6 mwb Magnet source Tooth/core back S1, S2, S3 & S4 Air gap Sgap Magnet Smag

Lumped circuit + GA made this design - 1.

28 Lumped circuit + GA made this design /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?

29 The only way forward seemed to be optimisation with 3D FE in the loop We need to get the leakage flux right needs 3D We 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?

30 PM machines new freedoms Modern PM s very powerful extreme example TG makes ampturns would need 400mm magnet depth would fit! Magnet strength prop depth winding strength with area at small sizes magnet has massive advantage Magnets don t conduct (much!) Magnets are not permeable Magnets have fixed pole number Can take terrible liberties with magnetic and electric circuit!

31 Explosion in methods of construction - Its all about nonoverlapped coils Non-overlapped coils let you tear the motor apart Make the end windings shorter Allow slots to be fully filled even with full automation

32 Single Tooth Segment Approach to Machine Construction (Sheldon 1954)

33 Overlapped coils - >= 1 slot/pole/phase pitch, distribution, sine waves 25-40% slot fill manual or complicated winding machines Non-overlapped to 0.5 slots/pole/phase - harmonics 60-80% slot fill bobbin winding - simple - flexible

34 Panasonic servo motors

35 Yamada s Patent of 1998

36 Further Core Splitting Techniques Yaskowa separate tooth and core backs Mitsubishi Poki-Poki Half lapped core back joints with clench pivot

37 Slip on coils over the core back

38 Mk 1

39 Mk 2 Shear stress = N/m 2 Centrifugal stress = 1227 g

40 Little men laminations Coil slips onto teeth

41 Core wraps up - open circuit field

42 All harmonics including the even harmonics F 2 = π n 1 n sin nβ 2, β = coil span Losses in the magnet for PM Disaster for an IM!

43 80mm frame size induction motor Two stators displaced 180 o wound backwards kills even harmonics But! zig-zag is very high

44 Mk 2 non-overlapped with tooth splits

45 No load with tooth splits mag. Current increased slightly

46 Rotor driven leakage flux Still lots of zig-zag

47 Torque (Nm) Conventional MK 1 non-overlapped Mk 2 non-overlapped rpm Torque-slip curves Still some work to do!

48 Some Switched Reluctance stuff SR s are simple, rugged, motor is cheap But Electronics is more expensive Noisy Motor is bigger than PM (but smaller then IM)

49 What s new in SR s segmented rotor Conventional 12/8 SR = 22.5Nm Segmented 12/10 SR = 32Nm PM 12/8 = 42Nm

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

51 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 DC Most domestic products driven by Universal motor It s the cost of the electronics!

52 To Conclude: If electronics cost next to nothing (big if!!!): IM looses all round SRM might win some PM wins (if magnets keep falling in price!) The biggest motor challenge bar none is to get the cost of the electronics down But - lots more fun to be had with machines!

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