Document 198259
Advances in Electric Machines: Topology, Materials and Construction Alan Jack University of Newcastle upon Tyne Newcastle Drives and M achines Group 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! Newcastle Drives and M achines Group 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 Newcastle Drives and M achines Group 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 Newcastle Drives and M achines Group 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 Newcastle Drives and M achines Group 0,8 0,6 0,4 0,2 0 Somaloy 500 New SMC 0 2000 4000 6000 8000 H ( A/m) 80 C ore loss (W/kg) 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 ) SMC 1,8 1,6 1,4 1,2 1 70 60 50 40 30 20 Somaloy 500 Somaloy 550 NEW SMC Material Newcastle Drives and M achines Group 10000 12000 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 Newcastle Drives and M achines Group Let’s set some benchmarks Torque = 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 speed Ht tangential magnetic field strength – limited by armature current heating – very flexible depends on cooling and arrangement Torque fixes the volume of the machine Newcastle Drives and M achines Group Turbogenerators try very hard with cooling and speed Typical figures for hydrogen/water cooled Bn = 1T Ht = 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 M achines Group 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! Newcastle Drives and M achines Group Conventional 35,000 rpm universal motor stator Dyson 100,000 rpm vacuum cleaner motor SR motor Newcastle Drives and M achines Group 100,000 rpm appliance motor New motor Original motor 20,000 rpm Newcastle Drives and M achines 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 M achines Group Turbogenset high speed generator Typical configuration 30,000 rpm 8 poles 2kHz base frequency Terminal volts 800 to 1,300 volts Newcastle Drives and M achines 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 M achines Group Stator Newcastle Drives and M achines Group Magnets Peak power 2.2MW Peak force = 106 N Newcastle Drives and M achines Group Translator Newcastle Drives and M achines Group Enercon wind generator 4MW very slow = very big! Newcastle Drives and M achines Group Enercon generator in the nacelle Newcastle Drives and M achines Group The biggest bang for the buck 2 – can we do anything about the loadings Bn = 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? Newcastle Drives and M achines Group 2: drop the steel and use loads of magnets Bn 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 Newcastle Drives and M achines Group 3: Modulated pole machines – TFM, Claw Pole Claw Pole structure All poles see all of the mmf – electric loading proportional to pole number SMC Core Back Coil Magnets SMC Roto Shaft & Hub Newcastle Drives and M achines 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 M achines Group 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 Newcastle Drives and M achines Group It leaks all over the place! Tooth tips View Direction Axial SL A/G Air View Direction Radial towards axis of rotation SL END Rend SL INT 2 Upper portion Magnets SL INT 1 Lower portion Rotor Magnets Air gap leakage Flux, SL1 rL SL2 x s SL5 SL4 SL3 Newcastle Drives and M achines Group 0.04 Tooth/core back S1 , S2 , S3 & S4 Air gap Sgap 85.8 5.0 80.1 64.5 0.7 48.1 1.2 31.7 31.1 5.7 15.6 16.4 14 Magnet Newcastle Drives and M achines Group Smag Magnet source 357 141 357 141 57 14 14 91 60 136 1.4 0.9 3.3 13.9 19.8 2.3 Resultant Flux = 74.6 mWb 16.4 0.6 Winding source 43.5 41.2 21.5 7.6 4.2 3.3 1.2 0.7 0.04 5.0 14 14 14 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 M achines Group 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? Newcastle Drives and M achines Group PM machines – “new” freedoms Modern 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 advantage Magnets don’t conduct (much!) Magnets are not permeable Magnets have fixed pole number Can take terrible liberties with magnetic and electric circuit! Newcastle Drives and M achines Group 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 Newcastle Drives and M achines Group Single Tooth Segment Approach to Machine Construction (Sheldon 1954) Newcastle Drives and M achines Group Overlapped coils >= 1 slot/pole/phase pitch, distribution, sine waves 25-40% slot fill manual or complicated winding machines Non-overlapped 0.25 to 0.5 slots/pole/phase - harmonics 60-80% slot fill bobbin winding - simple - flexible Newcastle Drives and M achines Group Panasonic servo motors Newcastle Drives and M achines Group Yamada’s Patent of 1998 Newcastle Drives and M achines Group Further Core Splitting Techniques Yaskowa separate tooth and core backs Mitsubishi Poki-Poki Half lapped core back joints with clench pivot Newcastle Drives and M achines Group Slip on coils over the core back Newcastle Drives and M achines Group Mk 1 Newcastle Drives and M achines Group Mk 2 Shear stress = 1.4 . 104 N/m2 Centrifugal stress = 1227 g Newcastle Drives and M achines Group Little men laminations Coil slips onto teeth Newcastle Drives and M achines Group Core wraps up - open circuit field Newcastle Drives and M achines Group All harmonics including the even harmonics 2 F= π ∑ n 1 ⎛ nβ ⎞ sin ⎜ ⎟ n ⎝ 2 ⎠ , β = coil span •Losses in the magnet for PM •Disaster for an IM! Newcastle Drives and M achines Group 80mm frame size induction motor Two stators displaced 180o wound backwards kills even harmonics But! zig-zag is very high Newcastle Drives and M achines Group Mk 2 non-overlapped with tooth splits Newcastle Drives and M achines Group No load with tooth splits mag. Current increased slightly Newcastle Drives and M achines Group Rotor driven leakage flux Still lots of zig-zag Newcastle Drives and M achines Group Conventional MK 1 non-overlapped Mk 2 non-overlapped Torque (Nm) 8 6 4 2 0 0 500 1000 1500 rpm Torque-slip curves Still some work to do! Newcastle Drives and M achines Group 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) Newcastle Drives and M achines Group What’s new in SR’s segmented rotor Conventional 12/8 SR = 22.5Nm Segmented 12/10 SR = 32Nm PM 12/8 = 42Nm Newcastle Drives and M achines Group What’s new in SR’s 2: – flux switching - Black and Decker Circular saw motor Newcastle Drives and M achines 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 DC Most domestic products driven by Universal motor It’s the cost of the electronics! Newcastle Drives and M achines Group 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! Newcastle Drives and M achines Group
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