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# Et4117 electrical machines and drives lecture4

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### Et4117 electrical machines and drives lecture4

1. 1. 1Challenge the futureOverview Electrical Machines andDrives• 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
2. 2. 2Challenge the futureDC Machines• Introduction, construction (4.2)• Principle of operation and basic calculations (4.2)• air gap flux density (1.1)• armature turn voltage and commutation (4.2.2)• armature windings (4.2.3)• total armature voltage (4.2.4)• torque (4.2.5)• magnetisation curve (4.2.6)• Armature reaction, interpoles, compensating winding (4.3)• Characteristics, means to control speed (4.4)• DC machine drives (4.5)• PMDC machines / PCB machines (4.6, 4.7)
3. 3. 3Challenge the futureAssumptions for calculations• steady state (mechanical and electrical)• the air gap is so small that the flux density does not change inradial direction• the air gap is so small that the flux density crosses the air gapperpendicular• iron losses are negligible• the magnetic permeability of iron is infinite
4. 4. 4Challenge the futureAir gap flux density• The field winding around one pole has Nf turns and carries acurrent If• Calculate the air gap flux density between the poles and the rotor
5. 5. 5Challenge the futureFlux densitygffglINB 0µ=ffgg INlH 22 =d dm mC SH s J n Aτ⋅ = ⋅∫ ∫∫
6. 6. 6Challenge the futureFlux density• Sketch flux linkage of aturn on the rotor• Calculate the maximumvoltage induced in turnfrom Faraday’s law
7. 7. 7Challenge the futureArmature turnvoltagevlBlrBtlrBtlrBrBtlAnBtteeSt)(2)(2dd)(dd)(d)(dddddddθωθθπθθθθθλπθθ==+−=−=⋅==∫∫∫+At θ=0, the flux linkage isminimum
8. 8. 8Challenge the futureCommutator asrectifier
9. 9. 9Challenge the futureCommutationCommutating coil ininterpolar region: noinduced voltage
10. 10. 10Challenge the futureArmature windings• English: turn, coil, winding• Dutch: winding, spoel, wikkeling
11. 11. 11Challenge the futureMechanical and electrical angles2e mpθ θ=2e mpω ω=
12. 12. 12Challenge the futureDC Machines• Introduction, construction (4.2)• Principle of operation and basic calculations (4.2)• air gap flux density (1.1)• armature turn voltage and commutation (4.2.2)• armature windings (4.2.3)• total armature voltage (4.2.4)• torque (4.2.5)• magnetisation curve (4.2.6)• Armature reaction, interpoles, compensating winding (4.3)• Characteristics, means to control speed (4.4)• DC machine drives (4.5)• PMDC machines / PCB machines (4.6, 4.7)
13. 13. 13Challenge the futureArmature voltage)(2 θω Blre mt =)(2 θω Blre mt =)(2d)(d/20θπθθπBrlprBlAnBp==⋅=Φ ∫∫∫mtpe ωπΦ=mamta KaNpeaNE ωωπΦ=Φ==An armature winding has N turnswith a parallel pathsand therefore N/a series-connected turnsFor the turn voltage, we foundThe average is lower:Flux per poleUsing this, the turn voltage is given byTherefore
14. 14. 14Challenge the futureVoltage and torque from powerbalanceddaa a mIU RI L Ktω= + + ΦCu f mechP P P P= + +2 ddaa a a a a mIP UI RI I L I Ktω= = + + ΦPower balance:Thereforemecha amPT K Iω= = Φ
15. 15. 15Challenge the futureElectromagnetic torque from LorenzaIlBlIBF acc )()( θθ ==aIrlBrFT acc )(θ==aac IapaIrlBT Φ==πθ2)(aaac IKIaNpTNT Φ=Φ==π2aaaamm IEIKTP =Φ== ωωLorenz force gives the same result as power balance.
16. 16. 16Challenge the futureMagnetic circuitWhich part saturates first?Why?
17. 17. 17Challenge the futureMagnetization curveWhy is this not a straight line?Why does it not start from zero?
18. 18. 18Challenge the futureDC 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)• PMDC machines / PCB machines (4.6, 4.7)
19. 19. 19Challenge the futureArmature reaction• Section 4.3 (Sen) has the title “DC generators”• DC machines are hardly used as generators• The operating principles are the same in motoring andgenerating• Therefore, we only look at constructional aspects of DCmachines discussed in 4.3, which are present in DC motors aswell as in DC generators:• compensating winding (Dutch: compensatiewikkeling)• interpoles (Dutch: hulppolen)• Both are related to armature reaction
20. 20. 20Challenge the futureArmature reaction
21. 21. 21Challenge the futureConsequencesarmaturereaction• Saturation• Commutation problems
22. 22. 22Challenge the futureCompensation winding• Saturation problem reduced• Expensive; only applied in machines that are often heavily loaded.Why in these machines?
23. 23. 23Challenge the futureInterpolesArmature reactionproduces a fluxdensity in theinterpolar region, sothat a voltage isinduced in thecommutating coil.This voltage opposescommutation.Interpoles reverse thedirection of this fluxdensity to induce avoltage thatacceleratescommutation.
24. 24. 24Challenge the futureDC 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)• Connections of DC machines• Separately excited DC machine• Series connected DC machine• DC machine drives (4.5)• PMDC machines / PCB machines (4.6, 4.7)
25. 25. 25Challenge the futureConnections of DC machines
26. 26. 26Challenge the futureSeparately excited DC machinesHow to control speed?Calculate no-load speed and stall torque.Φ= ama KE ωaa IKT Φ=aaat EIRU +=Pole flux does not depend onarmature voltage and load2)( Φ−Φ=Φ−Φ=aaaaaaamKTRKUKIRKUω
27. 27. 27Challenge the futureTorque speed characteristic• Where are motor, generator and plugging operation?• Speed control by means of• Voltage control: what happens if the voltage is increased?• Field control: what happens if the current is increased?• Resistance control: old-fashioned
28. 28. 28Challenge the futureVoltage control
29. 29. 29Challenge the futureField controlAre thecharacteristicsof (c) parallel?
30. 30. 30Challenge the futureSeries DC machine (universal motor)What happens to the speed when the torque is zero?21 aaaa IKKIKT =Φ=aIK1=Φ Neglecting saturation!
31. 31. 31Challenge the futureSeries DC motor11t amaaU RK KK K Tω = ± −212121)( maataaaaaKKRUKKIKKIKTω+==Φ=maataKKRUIω1+=maaaamaaaaaat IKKIRKIREIRU ωω 1+=Φ+=+=21 aaaa IKKIKT =Φ=aIK1=Φ
32. 32. 32Challenge the futureDC 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)
33. 33. 33Challenge the futureOverview Electrical Machines andDrives• 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