3ADW000547R0301 DC fundamentals en c DC machines Introduction Design Separately excited DC machine DC drive General Armature converter Control structure November 18 2022 Slide 2 ID: 1002075
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1. Thomas vinzDCS880DC fundamentals3ADW000547R0301 DC fundamentals en c
2. DC machines:Introduction.Design.Separately excited DC machine.DC drive:General.Armature converter.Control structure.November 18, 2022Slide 2Contents
3. DC machinesNovember 18, 2022Slide 3DC machines highlightsDC machines are well known forFull torque from zero speed.Wide field weakening range.Excellent control behavior.Correlation for controlField current and armature current are responsible for torque.Armature voltage and armature current are responsible for power.DC machines have half size compared to Standard AC machines.Introduction, highlights
4. DC machinesNovember 18, 2022Slide 4Introduction, torque and power compared to sizePower is equalTorque is equalP = 11 kWn = 1140 rpmM = 76 NmP = 11 kWn = 960 rpmM = 110 NmP = 11 kWn = 730 rpmM = 150 NmP = 22 kWn = 1440 rpmM = 150 NmP = 15 kWn = 960 rpmM = 150 NmP = 11 kWn = 730 rpmM = 150 Nm
5. DC machinesNovember 18, 2022Slide 5Stator of a DC machine (field)The stator is the stationary part.It provides the field (flux).Main poles are the field windings.Interpole and compensation windings eliminate unwanted effects.Design, stator
6. DC machinesNovember 18, 2022Slide 6Magnetic field in a DC machineThis is a stator of a 2-pole machine.Field winding generates an electro-magnetic field between the poles.Design, magnetic fields
7. DC machinesNovember 18, 2022Slide 7Rotation, motion and torqueBrushes and conductors must be implemented.Current in brushes and conductors is required to generate a second electro-magnetic field.The force between the two electro-magnetic fields generates the torque.Design, magnetic fields Brushes
8. DC machinesNovember 18, 2022Slide 8Interpole windingsThe inductance in the armature circuit affects the electro-magnetic-field.The interpole windings generate an opposite electro-magnetic field. This leads to a smoother commutation.Design, interpole windings nIanN-1/2 Ia1/2 IatIa
9. DC machinesNovember 18, 2022Slide 9Effect of compensation windingsThe compensation windings carry rotor current.The compensation windings neutralize the effect of unwanted flux (e.g., armature reaction).The compensation windings prevent magnetic saturation in the stator.Thus, it is possible to operate the machine at higher loads.Design, compensation windings
10. DC machinesNovember 18, 2022Slide 10Field weakening factor 1 : 5Field weakening factor1 : 3Design, compensation windings
11. DC machinesNovember 18, 2022Slide 11Sum up windingsField windingsCreate an electro-magnetic field.Used for flux.Interpole windingsPrevent uneven field. This leads to a smoother commutation.Compensation windingsPrevents magnetic saturation.Increases field weakening range.Design, windings
12. DC machinesNovember 18, 2022Slide 12Rotor of a DC machine (armature)The rotor is the moving part.It develops the torque.It contains the armature winding.The shaft is the center axis.The commutator connected with the windings.Design, rotor
13. DC machinesNovember 18, 2022Slide 13Commutator of a DC machineThe commutator is used to transfer the energy.The fins are connected to the windings.The brushes provide the electrical contact.The neutral zone is perpendicular to the main field.Design, commutator
14. DC machinesNovember 18, 2022Slide 14CompactnessCan be used as motor and generator.The shaft is mounted between bearings.The terminal box is used to connect the cables.Design, ABB machine
15. DC machinesNovember 18, 2022Slide 15The terminal box includes connectors.Non drive side with commutator, analog tacho or encoder.Middle part with the windings.Drive side with the shaft.Design, ABB machine
16. DC machinesNovember 18, 2022Slide 16Typical variantsAir-cooled variantIC 06IP 23Water-cooled variantIC 86WIP 54 or IP 55Design, ABB machine
17. DC machinesNovember 18, 2022Slide 17CharacteristicsBoth, armature and field are supplied by a separate power source.Formulas:Separately excited DC machineRAUAIAEMFLAArmatureExcitationUFIFEquivalent circuit diagram:c = ConstantT = Torque = FluxdtdIAEMF = UA - RA * IA – LA * T = c * IA * Φn =c * EMFΦ
18. DC machinesNovember 18, 2022Slide 18Field weakening factor:Commutation limitnbasenmaxUNUAINIAINIfTNTPNPnArmature voltageArmature currentField currentTorqueOutput powerf =nmaxnbaseCommutation limitSeparately excited DC machineField weakening area
19. DC drivesNovember 18, 2022Slide 19With external excitationGeneral layoutMV/LV transformer.Armature circuitAC fuses.Mains contactor.Line reactor.Armature converter.DC fuses.Field circuit.Field fuses.Autotransformer.Field contactor.Field converter.General, layout~~--LoadMV lineMV/LV transformerMains contactor (K1)AC fuses (F1)Line reactor (L1) Field fuses (F3)Armature converterDC fusesField windingField contactor (K3)Field converterAutotransformer (T3)M
20. DC drivesNovember 18, 2022Slide 20DC currentAC line current3 AC network1 3 54 6 2UdIdiLL1uL~~~L3L2NControlled voltage source depending on firing angle The output voltage can be positive or negativeGeneral, 6-pulse thyristor bridge (line commutated) Mainsvoltage
21. DC drivesNovember 18, 2022Slide 21DC current and AC currentRelationship between AC and DC current:Example with a motor load (2-Q):Line reactors, cables, contactors and fuses must be selected depending on the RMS values!Armature converter, calculations 1000 V
22. DC drivesNovember 18, 2022Slide 22Generating output voltageVoltagesPhase voltage (L1, L2, L3).Phase to phase voltage (e.g., L12).Thyristor 1 and 6 are active.The output bubble is shown in red.Armature converter, output voltage 3 AC network 1 3 54 6 2UdIdiLL1uL~~~L3L2
23. DC drivesNovember 18, 2022Slide 23How a thyristor converter works Armature converter, output voltage6-pulse thyristor bridge with a loadFiring sequence:Thyristor 1 + 6Thyristor 2 + 1Thyristor 3 + 2Thyristor 4 + 3Thyristor 5 + 4Thyristor 6 + 53 ~ AC network1 3 54 6 2UdaIdiLL1uL~~~L2L2
24. DC drivesNovember 18, 2022Slide 24Machine is motoringPositive voltageThe firing angle is < 90°.The minimum firing angle is 15°.The natural firing angle ( = 0°) is the intersection between two phases.In this example the thyristor is fired after 30° ( = 30°) from the natural firing angle.Armature converter, driving mode = 30°
25. DC drivesNovember 18, 2022Slide 25Machine is generatingNegative voltageThe firing angle > 90°.The maximum firing angle is 150°.Armature converter, regenerative mode = 150°
26. DC drivesNovember 18, 2022Slide 26Commutation failureDC drives can be compromised by a commutation failure causing:Damaged fuses.Damaged thyristors.Causes of a commutation failure:Mains power failure.Too high firing angles.Thus, the working range of the B6-bridge must be limited. With typical firing angles between 15°and 150°.Armature converter, commutation failure or shoot-throughBalancing voltageFiring angle
27. DC drivesNovember 18, 2022Slide 27Commutation failure begins near firing angles of 180°, so typically the firing angles are limited between 15° and 150°Commutation failure is more likely with 4-Q drives compared to 2-Q drives. In 2-Q drives the condition will merely cause a loss in output voltage. In 4-Q drives, however, a severe overcurrent will occur. Commutation failure will cause very high current flow through motor, DC-breaker (if present), thyristors and fuses. It can cause damage to the motor, thyristors and fuses.Commutation failures usually happens while regenerating. The common causes are:Loss of mains or a mains power dip.Poor mains quality (too soft mains and thus wide commutation notches).Excessive armature voltage.Failure or malfunction of a firing pulse circuit.Armature converter, commutation failure or shoot-through
28. DC drivesNovember 18, 2022Slide 28DC currentIdDC current in one thyristor branch(120° width)IV2, IV3, IV4 AC current in the mains(120° = Id and 60° = 0)IL1, IL2, IL3 Armature converter, current in a DC drive
29. DC drivesNovember 18, 2022Slide 29Udα calculation for a 2-Q driveFiring angle between 15° and 150°.Maximum save DC voltage:150° because of commutation (current) and recovery (thyristor).15° because of safety, due to mains voltage jitter.0.9 safety factor for 10 % mains voltage drop.Armature converter, voltage of a 2-quadrant (2-Q) drive Voltage source characteristic:UdUd cos Maximum firing angle
30. DC drivesNovember 18, 2022Slide 30Udα calculation for a 4-Q driveFiring angle between 15° and 150°.Maximum save DC voltage:150° because of commutation (current) and recovery (thyristor).15° because of safety, due to mains voltage jitter.0.9 safety factor for 10 % mains voltage drop.Armature converter, voltage of a 4-quadrant (4-Q) drive Positive voltage source characteristic:UdUd cos Maximum firing angleNegative voltage source characteristic:UdUd cos Maximum firing angle
31. DC drivesNovember 18, 2022Slide 31Principle circuit diagram:UdLARAEMK ~ n, IF Ud ∼ cosIAContinuous currentDiscontinuous currentArmature converter, continuous and discontinuous armature current
32. DC drivesNovember 18, 2022Slide 32QuadrantsThe convention for a Cartesian coordinate system isThe 1st quadrant is on the top right.All other numbers follow counterclockwise.Thus follows:Armature converter, quadrantsIIIIIIIVYXQuadrantIIIIIIIVx-coordinate> 0< 0< 0> 0y-coordinate> 0> 0< 0< 0
33. DC drivesNovember 18, 2022Slide 33Typical applications:Extruder.Mixer.Rod and bar mills.MUdIdIIActive brakingIDrivingIIIDrivingIVBrakingSpeed (voltage)Torque(current)Armature converter, single bridge (2-Q)
34. DC drivesNovember 18, 2022Slide 34IIActive brakingIDrivingIIIDrivingIVBrakingSpeed (voltage)Torque(current)Typical applications:Ski lifts.Test rigs.Winder.For smooth and fast torque reversal.MUdIdArmature converter, single bridge (4-Q)
35. DC drivesNovember 18, 2022Slide 35Typical applications:MixerPropulsionSlow changeover of torque. Thus, less control performanceUseable if P > 500 kWIIActive brakingIDrivingIIIDrivingIVBrakingSpeed (voltage)Torque(current)MUdIdArmature converter, (2-Q) with field reversal
36. DC drivesNovember 18, 2022Slide 36VoltageThere is a voltage limitation in quadrants II and IV.The maximum firing angle is limited to 150° since the thyristors need a recovery time β of 30°.This reduces the motor voltage in a 4-Q drive.2-Q drives cannot be used for active braking (positive speed direction). Thus, the motor voltage can be higher.Armature converter, maximum regenerative/generating voltageMaximum generating voltageIIActive brakingIDrivingIIIDrivingIVBrakingSpeed (voltage)Torque(current)
37. Armature converter, overviewDC drivesNovember 18, 2022Slide 37MainsLine reactorThyristor bridgeLoad1 3 54 6 2iCEMFUdIdiLXLuL~~~
38. DC drivesNovember 18, 2022Slide 38Commutation in a converterCommutation from one thyristor to the next thyristor.The commutation leads to a:Short circuit of the phase voltage at the point of common connection (PCC).Short circuit of the current at the point of common connection (PCC)..The line reactors limit the depth (u) and length (t) of the commutation notches.Armature converter, commutation3 ~ AC network1 3 54 6 2UdIdiLL1uL~~~L3L2Line reactorsukPCCtuPhase voltage
39. DC drivesNovember 18, 2022Slide 39Purpose of line reactorsLimit the di/dt during commutation.Prevent interferences between drives connected to the same line and other upstream connected equipment.Each converter gets its own line reactor!When thyristor converters operate, the line voltage is short-circuited during commutation from one thyristor to the next. Line reactors are used to reduce the commutation spikes to the upstream supply.Line reactors lead to a reduction of the maximum available output voltage, due to their voltage drop.Armature converter, line reactors
40. DC drivesNovember 18, 2022Slide 40ConfigurationsOne line reactor per driveuK = 1 % or 4 %.Dedicated transformer One transformer per drive, typically used for large drives. uK = 1 % to 10 %.Armature converter, line reactorsMMM
41. DC drivesNovember 18, 2022Slide 41ConfigurationsAutotransformerRequires an additional line reactor.uK = 1 % or 4 %.H8 drives Maximum two drives per transformer. uK = 1 % to 10 %.Armature converter, line reactorsMMMAux. voltage
42. DC drivesNovember 18, 2022Slide 42Control structure, diagram
43. November 18, 2022Slide 43