WO2017025142A1 - A synchronous machine and a method for operating the machine - Google Patents

A synchronous machine and a method for operating the machine Download PDF

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Publication number
WO2017025142A1
WO2017025142A1 PCT/EP2015/068639 EP2015068639W WO2017025142A1 WO 2017025142 A1 WO2017025142 A1 WO 2017025142A1 EP 2015068639 W EP2015068639 W EP 2015068639W WO 2017025142 A1 WO2017025142 A1 WO 2017025142A1
Authority
WO
WIPO (PCT)
Prior art keywords
winding
rotor
stator
synchronous machine
harmonics
Prior art date
Application number
PCT/EP2015/068639
Other languages
French (fr)
Inventor
Jan Westerlund
Jari Jäppinen
Original Assignee
Abb Schweiz Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Abb Schweiz Ag filed Critical Abb Schweiz Ag
Priority to PCT/EP2015/068639 priority Critical patent/WO2017025142A1/en
Publication of WO2017025142A1 publication Critical patent/WO2017025142A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H02K19/02—Synchronous motors
    • H02K19/10—Synchronous motors for multi-phase current
    • H02K19/12—Synchronous motors for multi-phase current characterised by the arrangement of exciting windings, e.g. for self-excitation, compounding or pole-changing
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K11/00—Structural association of dynamo-electric machines with electric components or with devices for shielding, monitoring or protection
    • H02K11/04—Structural association of dynamo-electric machines with electric components or with devices for shielding, monitoring or protection for rectification
    • H02K11/042—Rectifiers associated with rotating parts, e.g. rotor cores or rotary shafts
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K19/00—Synchronous motors or generators
    • H02K19/16—Synchronous generators
    • H02K19/26—Synchronous generators characterised by the arrangement of exciting windings
    • H02K19/28—Synchronous generators characterised by the arrangement of exciting windings for self-excitation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K3/00—Details of windings
    • H02K3/04—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors
    • H02K3/18—Windings for salient poles
    • H02K3/20—Windings for salient poles for auxiliary purposes, e.g. damping or commutating

Definitions

  • the invention relates to a synchronous machine and to a method for operating the machine.
  • the synchronous machine can be a synchronous motor or a synchronous generator.
  • AVR automatic voltage regulator
  • US patent 6,051 ,953 discloses one example of a brushless synchronous machine with two stator windings.
  • the stator contains two windings i.e. a main winding and an auxiliary winding to generate harmonics into the air gap between the stator and the rotor.
  • the auxiliary winding requires an additional power supply device or rectifier bridge.
  • the rotor consists also of two complex winding systems that in general increase the total costs of these machine types. There is no need for a separate exciter in this arrangement.
  • the stator winding generate simultaneously the main working gap harmonic which is responsible for the electromagnetic torque, and also a specific high harmonic which is used for the excitation of the rotor winding.
  • the rotor consists of two windings i.e. the excitation winding and the field winding. When the rotor rotates, electromagnetic forces are induced in the excitation winding. The magnitude of these electromagnetic forces depends on the magnetic field in the air-gap harmonics.
  • the induced electromagnetic forces in the rotor excitation winding are rectified with a diode bridge circuit so that a direct current flows into the field winding.
  • a special connection for the winding coils for the field winding may be chosen.
  • the invention is particularly related to a brushless synchronous machine without a separate exciter i.e. to a brushless self-exciting synchronous machine.
  • An object of the present invention is to achieve an improved synchronous machine.
  • the synchronous machine according to the invention is defined in claim 1 .
  • the synchronous machine comprises:
  • a stator comprising a stator winding
  • a rotating rotor comprising a rotor winding and an exciter winding disposed adjacent to an air gap formed between the stator and the rotor
  • a rotating DC power supply comprising a rectifier positioned on the rotor, the exciter winding being electrically coupled to an input of the DC power supply and an output of the DC power supply being electrically coupled to the rotor winding,
  • a voltage regulator electrically coupled to the stator winding, a harmonics injector connected via a transformer to a zero point of the stator winding, whereby the harmonics injector is controlled by the voltage regulator to inject a harmonics distortion into the stator winding, said harmonics distortion being induced from the stator winding to the exciter winding in the rotor and thereby to the input of the DC power supply, said harmonics distortion being rectified in the rectifier of the DC power supply and supplied as DC current to the stator winding from the output of the DC power supply.
  • the method for operating a synchronous machine comprises the steps of:
  • a passive rectifier bridge can thus be used in the rotor in order to rectify the AC current from the exciter winding into DC current to be supplied into the rotor winding.
  • the harmonics injector can be controlled to inject a current and/or voltage having a desired amplitude and frequency to the stator winding.
  • the AVR measures the electric conditions e.g. the voltage and/or the current in the stator winding.
  • the invention makes it possible to control the excitation of a directly to the power grid connected synchronous machine without any major changes to the rotor bridge and/or to the power electronics of the synchronous machine.
  • the damper winding in the rotor of the synchronous machine could be designed so that it is suitable to receive excitation from the stator winding.
  • the harmonics injector connected to the zero point of the stator winding could be protected against possible over voltages if there is a need for this.
  • the harmonics injector may be directly integrated into the synchronous machine or the harmonics injector may be a separate unit outside the electric machine in case the zero point of the stator winding has been brought outside the machine.
  • the stator winding generate simultaneously the main working air- gap harmonic which is responsible for the electromagnetic torque, and also a specific harmonic which is used for excitation of the rotor winding.
  • Figure 1 shows a longitudinal cross section of a synchronous machine
  • Figure 2 shows a traverse cross section of the synchronous machine
  • Figure 3 shows a cross section of one pole in the rotor and the corresponding portion of the stator in the synchronous machine
  • Figure 4 shows a DC power supply that can be used in the rotor of the synchronous machine
  • Figure 5 shows a first embodiment of the invention
  • Figure 6 shows a second embodiment of the invention.
  • Fig. 1 shows a longitudinal cross section
  • Fig. 2 shows a traverse cross section of a synchronous machine.
  • the synchronous machine 400 comprises a longitudinal centre axis X-X, a cylindrical rotor 100 and a cylindrical stator 200 surrounding the rotor 100.
  • the longitudinal centre axis X- X of the rotor 100, the stator 200 and the synchronous machine 400 coincide.
  • the rotor 100 comprises a centre portion 1 10 provided with a rotor winding 1 1 1 and two end portions 120, 130 at each axial X-X end of the centre portion 1 10. Each end portion 120, 130 of the rotor 100 is rotatably supported on a bearing 140, 150.
  • the rotor 100 may be a salient pole rotor, whereby each pole comprises a pole body 1 12 and a pole shoe 1 13 at the radial outer end of the pole body 1 12. The radial inner end of the pole body 1 12 is attached to a shaft 1 15 of the middle portion 1 10 of the rotor 100.
  • the rotor winding 1 1 1 is wound around the pole body 1 12 so that the winding wire passes in the axial X-X direction on a first axial X-X side of the pole body 1 12 and returns on a second opposite axial X-X side of the pole body 1 12.
  • the pole body 1 12 and the pole shoe 1 13 are formed as one single entity.
  • the stator 200 comprises a stator core 210 and a stator frame 220 surrounding the stator core 210.
  • the stator core 210 is attached to the stator frame 220 and the stator frame 220 is supported on a support structure 300.
  • the stator core 210 can be attached with e.g. welding or with compression joints to the stator frame 220.
  • the stator core 210 is further provided with a stator winding 21 1 having winding ends 21 1A at each axial X-X end of the stator 200 shown in figure 1 .
  • the stator core 210 comprises slots 212 penetrating into the stator core 210 from the inner perimeter of the stator core 210.
  • the slots 212 in the stator core 210 receive the stator winding 21 1 .
  • the stator core 210 may have a laminated structure being composed of annular sheets that are stacked together to form the stator core 210.
  • the sheets are grouped into a number of groups in the axial X-X direction of the stator 200. Each group is separated by an air duct sheet, whereby radial air channels extending from an inner perimeter of the stator core 210 to an outer perimeter of the stator core 210 are formed by the air duct sheets.
  • Each annular sheet in the stator core 210 can be made of sectors 21 OA, 210B, whereby the sectors 21 OA, 210B are attached to each other in order to form a closed perimeter.
  • the stator core 210 comprises further back beams 213 attached to the outer surface of the stator core 210 and extending in the axial X-X direction of the stator 200.
  • the stator core 210 has a cylindrical form.
  • the stator frame 220 is only schematically shown in the figure.
  • the stator frame 220 may be made of end plates at both ends of the stator frame 220 and frame plates positioned at an axial X-X distance from each other along the centre axis X-X of the synchronous machine 400 between the end plates.
  • the frame plates may be attached to the stator core 210 and to a support structure 300 supporting the synchronous machine 400.
  • the frame plates can be formed of continuous frame plates extending around the perimeter of the stator core 210 or of separate sectors positioned symmetrically along the perimeter of the stator core 210.
  • the frame plates in each sector are then attached to each other with axially X-X along an outer perimeter of the frame plates extending connection parts.
  • the connection part and the frame plates in a sector form a frame plate package.
  • the axial X-X ends of the frame plate packages may be attached to a respective end plate with fastening means e.g. with bolts and nuts.
  • the inner perimeter of the transverse cross section of the stator frame 220 may be of a circular form.
  • the outer perimeter of the transverse cross section of the stator frame 220 may be of any form e.g. of a polygonal form.
  • the stator core 210 and the stator frame 220 can thus be manufactured independently simultaneously.
  • the annular sheets of the stator core 210 are assembled to form the complete stator core 210 and then the stator winding 21 1 is wound into the slots 212 in the stator core 210.
  • the stator frame is assembled from the end plates and the frame plates to form the complete stator frame 220.
  • the stator core 210 is then attached to the stator frame 220. This can be done e.g. by L-shaped brackets.
  • One branch of the brackets may be fastened with compression joints to the back beams 213 and the other branch may be fastened with compression joints to the frame plates.
  • the compression joints in both branches can be achieved e.g. with bolts and nuts.
  • Another possibility would be to use C-clamps on the back beams 213 and to attach the C-clamps by welding to the back beams 213 and the frame plates.
  • the synchronous machine 400 comprises further a connection space 250 within the synchronous machine 400.
  • the connection space 250 may be formed as a separate box attached to the stator frame 220 or as an integral part of the stator frame 220.
  • the stator winding 21 1 is connected to output terminals in the connection space 250.
  • the synchronous machine 400 comprises further an automatic voltage regulator (AVR) 500 for regulating the voltage of the synchronous machine 400.
  • AVR automatic voltage regulator
  • Fig. 3 shows a cross section of one pole in the rotor and the corresponding portion of the stator in the synchronous machine.
  • a single phase harmonics exciter winding 1 16 is shown in the figure.
  • the number of exciter winding slots 1 17 is advantageously in the range of 1 .8 to 2.2 times, advantageously 2 times the number of stator winding slots 212 in a given sector for a single phase energy harvesting exciter winding 1 16.
  • the pitch of the exciter winding slots 212 is in the range of 1 .8 to 2.2 times, advantageously 2 times denser than the pitch of the stator winding slots 212.
  • the exciter winding 1 16 is formed of axially extending damper bars positioned in the outer surface of the pole shoe 1 13 adjacent to the air gap G1 between the rotor 100 and the stator 200.
  • the exciter winding 1 16 in the rotor 100 has been designed to receive excitation from the stator winding 21 1 .
  • AC harmonics frequencies above the nominal frequency of the synchronous machine are injected into the stator winding 21 1 so that said harmonics frequencies induce an AC current to the exciter winding 1 16 in the rotor 100 of the synchronous machine.
  • the exciter winding 1 16 in the rotor 100 is designed to be compatible with the stator winding 21 1 at the injected harmonics frequencies. The idea is that only the injected harmonics frequencies in the stator winding 21 1 induce an AC current in the exciter winding 1 16.
  • the plurality of exciter windings 1 16 may be disposed within the pole 1 12, 1 13 of the rotor 100 at the radial outer edge of the shoe 1 13 of the pole 1 12, 1 13.
  • the rotor 100 is a salient pole rotor, having field windings 1 1 1 disposed inwardly relative to the pole shoe 1 13 around the pole body 1 12.
  • the harmonics exciter winding 1 16 is spaced every 180 electrical degrees.
  • the exciter windings 1 16 can be disposed in slots 1 17 that are open towards the air gap G1 .
  • the slots 1 17 can include only exciter windings 1 16 or the slots 1 17 could also include the field winding 1 1 1 , damper bars, or other auxiliary windings. Additional slots can be included on the pole shoe 1 13 that contain exciter windings 1 16 in addition to damper bars or other windings.
  • Figure 4 shows a DC power supply that can be used in the rotor of the synchronous machine.
  • the high frequency voltage induced from the stator winding 21 1 into the exciter winding 1 16 of the rotor 100 can be fed to a DC power supply 150 positioned on the rotor 100 of the synchronous machine 400.
  • the power supply 150 comprises a passive rectifier RB1 .
  • the alternating current AC1 , AC2, AC3, AC4 from the exciter winding 1 16 of the rotor 100 is fed to the input of the power supply 150.
  • the rectifier RB1 can be a multiphase passive rectifier including a full-wave diode bridge.
  • the rectifier RB1 converts the alternating current AC1 , AC2, AC3, AC4 at the input of the rectifier RB1 to a direct current DC1 at the output of the rectifier RB1 .
  • the injected harmonics have a higher frequency than the fundamental frequency of the synchronous machine, which means that fast switching diodes are preferred in the rectifier RB1 over conventional thyristors. However, new high frequency switching thyristors could be implemented in the power supply 150.
  • a rectifier RB1 based on a full wave diode bridge includes four fast switching diodes.
  • the power supply 150 supplies a controlled direct current DC1 from the output of the power supply 150 to the field windings 1 1 1 of the rotor 100.
  • the DC power supply 150 is a passive power supply i.e. there is no need to be able to control the DC power supply 150.
  • FIG. 5 shows a first embodiment of the invention.
  • the stator winding 21 1 of the synchronous machine 400 is connected directly to the power grid 600.
  • the automatic voltage regulator (AVR) 500 is connected to the stator winding 21 1 so that the AVR 500 receives measurement data of the electrical conditions at the terminals of the stator winding 21 1 .
  • the AVR 500 can, based on the measurement data, determine the current that is required in the rotor windings 1 1 1 in order to generate the desired field in the air gap G1 .
  • a harmonics injector 710 is connected via a current transformer 720 to the zero point or the star point of the stator winding 21 1 .
  • the harmonics injector 710 is configured to inject harmonics into the stator winding 21 1 .
  • the AVR 500 can indirectly control the current of the rotor windings 1 1 1 by controlling the harmonics injector 710 and thereby the injection of harmonics to the stator winding 21 1 .
  • the injection of harmonics into the stator winding 21 1 will induce an alternating current AC1 in the exciter winding 1 16 and the alternating current AC1 in the exciter winding 1 16 will be rectified by the rectifier RB1 into a direct current DC1 which is then fed into the rotor winding 1 1 1 .
  • FIG. 6 shows a second embodiment of the invention.
  • a voltage transformer 730 is used instead of the current transformer in this embodiment.
  • the voltage transformer connects the harmonics injector 710 to the zero point or star point of the stator winding 21 1 .
  • the harmonics injector 710 is connect to the primary side of the voltage transformer 730 and the secondary side of the voltage transformer 730 is connected to the zero point of the stator winding 21 1 .
  • a frequency converter can be used as the harmonics injector 710 in the invention.
  • the frequency converter 710 can be configured to inject harmonics into the stator winding 21 1 .
  • the AVR 500 will control the harmonics injector 710 and thereby the injection of harmonics into the stator winding 21 1 .
  • the frequency of the harmonics distortion could be kept constant, whereby the amplitude of the harmonics distortion could be regulated so that the desired excitation current in the rotor winding 1 1 1 is achieved at each time.
  • a current transformer 720 can be used when the current of the harmonics distortion is the quantity to be regulated.
  • a voltage transformer 730 can be used when the voltage of the harmonics distortion is the quantity to be regulated.
  • the frequency of the injected harmonics should be selected so that it induces well into the exciter winding 1 16.
  • Harmonics in an air gap of an open slot type line fed synchronous machine mainly contain slotting harmonics due to the large slot openings in the stator. Some of the slotting harmonics are normally significantly larger compared to the other slotting harmonics in the air gap.
  • the width of the exciter winding slots 1 17 should be about the same as the width of the stator winding slots 212. If some lower frequencies e.g. the 5 th order harmonics are utilized, then the width of the exciter winding slots 1 17 should be greater than the width of the stator winding slots 212.
  • the exciter winding slots 1 17 it is advantageous to dimension the exciter winding slots 1 17 so that the pitch of the exciter winding slots 1 17 is in the range of 1 .8 to 2.2 times, more advantageously 2 times denser than the pitch of the stator winding slots 212. This will result in that the slot harmonics of the stator 200 can be utilized to their full extent. It is also advantageous to use the same slot harmonics frequency as the supply frequency in the harmonics injector 710. This will result in that the injected harmonics will be transferred effectively from the stator winding to the exciter winding in the rotor.
  • the magnetic energy induced into the exciter winding can be regulated i.e. increased or decreased by regulating the phase angle and the amplitude of the injected harmonics.
  • the transformer 720, 730 provides galvanic isolation between the stator winding 21 1 and the harmonics injector 710.
  • the invention can be used in a synchronous machine having a star connected or delta connected stator winding.
  • the invention is not limited to a salient pole synchronous machine as disclosed in the figures, but can be used in any synchronous machine.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Synchronous Machinery (AREA)

Abstract

The synchronous machine comprises a stator (200) and a rotating rotor 100. The stator (200) has a stator winding (211) and the rotor (100) has a rotor winding (111) and an exciter winding (116) disposed adjacent to the air gap (G1). A DC power supply (150) comprising a rectifier (RB1) is positioned on the rotor (100), the exciter winding (116) being electrically coupled to an input of the DC power supply (150) and an output of the DC power supply (150) being electrically coupled to the rotor winding (111). A voltage regulator (500) is electrically coupled to the stator winding (211). A harmonics injector (710) is connected via a transformer (720) to a zero point of the stator winding (211). The harmonics injector (710) is controlled by the voltage regulator (500) to inject a harmonics distortion into the stator winding (211), said harmonics distortion being induced from the stator winding (211) to the exciter winding (116) in the rotor (100) and thereby to the input of the DC power supply (150), said harmonics distortion being rectified in the rectifier (RB1) of the DC power supply (150) and supplied as DC current to the stator winding (111) from the output of the DC power supply (150).

Description

A SYNCHRONOUS MACHINE AND A METHOD FOR OPERATING THE MACHINE
FIELD OF INVENTION
The invention relates to a synchronous machine and to a method for operating the machine. The synchronous machine can be a synchronous motor or a synchronous generator.
BACKGROUND
There are synchronous machines provided with brushes and brushless synchronous machines. Electric power is transferred via the brushes between the stationary stator and the rotating rotor in a synchronous machine provided with brushes. Electric power is on the other hand transferred with induction between the stationary stator and the rotating rotor in a brushless synchronous machine.
Many brushless synchronous machines are provided with a separate exciter. The exciter provides excitation power to the rotor winding of the synchronous machine. The stator of the exciter has electromagnet poles that are provided with power from a separate power stage in an automatic voltage regulator (AVR). By regulation of one or both of the voltage and frequency of the excitation on the stator of the exciter, the excitation of the synchronous machine can be indirectly regulated.
US patent 6,051 ,953 discloses one example of a brushless synchronous machine with two stator windings. The stator contains two windings i.e. a main winding and an auxiliary winding to generate harmonics into the air gap between the stator and the rotor. The auxiliary winding requires an additional power supply device or rectifier bridge. The rotor consists also of two complex winding systems that in general increase the total costs of these machine types. There is no need for a separate exciter in this arrangement.
There are further brushless synchronous machines with simple tooth concentrated windings for both the stator and the rotor. There is no need for an auxiliary winding in the stator and thereby also no need for the power supply and control unit of the auxiliary winding. The stator winding generate simultaneously the main working gap harmonic which is responsible for the electromagnetic torque, and also a specific high harmonic which is used for the excitation of the rotor winding. The rotor consists of two windings i.e. the excitation winding and the field winding. When the rotor rotates, electromagnetic forces are induced in the excitation winding. The magnitude of these electromagnetic forces depends on the magnetic field in the air-gap harmonics. The induced electromagnetic forces in the rotor excitation winding are rectified with a diode bridge circuit so that a direct current flows into the field winding. To avoid the high harmonics effect on the field winding, a special connection for the winding coils for the field winding may be chosen.
The invention is particularly related to a brushless synchronous machine without a separate exciter i.e. to a brushless self-exciting synchronous machine.
SUMMARY
An object of the present invention is to achieve an improved synchronous machine.
The synchronous machine according to the invention is defined in claim 1 .
The synchronous machine comprises:
a stator comprising a stator winding,
a rotating rotor comprising a rotor winding and an exciter winding disposed adjacent to an air gap formed between the stator and the rotor,
a rotating DC power supply comprising a rectifier positioned on the rotor, the exciter winding being electrically coupled to an input of the DC power supply and an output of the DC power supply being electrically coupled to the rotor winding,
a voltage regulator electrically coupled to the stator winding, a harmonics injector connected via a transformer to a zero point of the stator winding, whereby the harmonics injector is controlled by the voltage regulator to inject a harmonics distortion into the stator winding, said harmonics distortion being induced from the stator winding to the exciter winding in the rotor and thereby to the input of the DC power supply, said harmonics distortion being rectified in the rectifier of the DC power supply and supplied as DC current to the stator winding from the output of the DC power supply.
The method for operating the synchronous machine according to the invention is defined in claim 7.
The method for operating a synchronous machine comprises the steps of:
measuring the electrical conditions in a stator winding of the synchronous machine with a voltage regulator,
selecting a predetermined current level in a rotor winding of the synchronous machine based on the measured electrical conditions in the stator winding of the synchronous machine,
injecting a harmonics distortion to the stator winding of the synchronous machine with a harmonics distortion injector connected via a transformer to a zero point of a stator winding of the synchronous machine based on the predetermined current level in the rotor winding of the synchronous machine, whereby a current attributable to the harmonics distortion is induced in an exciter winding disposed in a rotor of the synchronous machine adjacent to an air gap formed between the rotor and the stator of the synchronous machine,
rectifying the current in the exciter winding, and
supplying the rectified current to the rotor winding, thereby effecting the predetermined current level in the rotor winding.
There is no need for a controllable rectifier bridge in the rotor in the invention. A passive rectifier bridge can thus be used in the rotor in order to rectify the AC current from the exciter winding into DC current to be supplied into the rotor winding. The harmonics injector can be controlled to inject a current and/or voltage having a desired amplitude and frequency to the stator winding. The AVR measures the electric conditions e.g. the voltage and/or the current in the stator winding.
The invention makes it possible to control the excitation of a directly to the power grid connected synchronous machine without any major changes to the rotor bridge and/or to the power electronics of the synchronous machine.
The damper winding in the rotor of the synchronous machine could be designed so that it is suitable to receive excitation from the stator winding.
The harmonics injector connected to the zero point of the stator winding could be protected against possible over voltages if there is a need for this.
The harmonics injector may be directly integrated into the synchronous machine or the harmonics injector may be a separate unit outside the electric machine in case the zero point of the stator winding has been brought outside the machine.
The stator winding generate simultaneously the main working air- gap harmonic which is responsible for the electromagnetic torque, and also a specific harmonic which is used for excitation of the rotor winding.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which
Figure 1 shows a longitudinal cross section of a synchronous machine,
Figure 2 shows a traverse cross section of the synchronous machine,
Figure 3 shows a cross section of one pole in the rotor and the corresponding portion of the stator in the synchronous machine,
Figure 4 shows a DC power supply that can be used in the rotor of the synchronous machine,
Figure 5 shows a first embodiment of the invention,
Figure 6 shows a second embodiment of the invention.
DETAILED DESCRIPTION
Fig. 1 shows a longitudinal cross section and Fig. 2 shows a traverse cross section of a synchronous machine. The synchronous machine 400 comprises a longitudinal centre axis X-X, a cylindrical rotor 100 and a cylindrical stator 200 surrounding the rotor 100. The longitudinal centre axis X- X of the rotor 100, the stator 200 and the synchronous machine 400 coincide.
The rotor 100 comprises a centre portion 1 10 provided with a rotor winding 1 1 1 and two end portions 120, 130 at each axial X-X end of the centre portion 1 10. Each end portion 120, 130 of the rotor 100 is rotatably supported on a bearing 140, 150. The rotor 100 may be a salient pole rotor, whereby each pole comprises a pole body 1 12 and a pole shoe 1 13 at the radial outer end of the pole body 1 12. The radial inner end of the pole body 1 12 is attached to a shaft 1 15 of the middle portion 1 10 of the rotor 100. The rotor winding 1 1 1 is wound around the pole body 1 12 so that the winding wire passes in the axial X-X direction on a first axial X-X side of the pole body 1 12 and returns on a second opposite axial X-X side of the pole body 1 12. The pole body 1 12 and the pole shoe 1 13 are formed as one single entity.
The stator 200 comprises a stator core 210 and a stator frame 220 surrounding the stator core 210. The stator core 210 is attached to the stator frame 220 and the stator frame 220 is supported on a support structure 300. The stator core 210 can be attached with e.g. welding or with compression joints to the stator frame 220. The stator core 210 is further provided with a stator winding 21 1 having winding ends 21 1A at each axial X-X end of the stator 200 shown in figure 1 .
There is an air gap G1 between the outer surface of the middle portion 1 10 of the rotor 100 and the inner surface of the stator core 210.
The stator core 210 comprises slots 212 penetrating into the stator core 210 from the inner perimeter of the stator core 210. The slots 212 in the stator core 210 receive the stator winding 21 1 . The stator core 210 may have a laminated structure being composed of annular sheets that are stacked together to form the stator core 210. The sheets are grouped into a number of groups in the axial X-X direction of the stator 200. Each group is separated by an air duct sheet, whereby radial air channels extending from an inner perimeter of the stator core 210 to an outer perimeter of the stator core 210 are formed by the air duct sheets. Each annular sheet in the stator core 210 can be made of sectors 21 OA, 210B, whereby the sectors 21 OA, 210B are attached to each other in order to form a closed perimeter. The stator core 210 comprises further back beams 213 attached to the outer surface of the stator core 210 and extending in the axial X-X direction of the stator 200. The stator core 210 has a cylindrical form.
The stator frame 220 is only schematically shown in the figure. The stator frame 220 may be made of end plates at both ends of the stator frame 220 and frame plates positioned at an axial X-X distance from each other along the centre axis X-X of the synchronous machine 400 between the end plates. The frame plates may be attached to the stator core 210 and to a support structure 300 supporting the synchronous machine 400. The frame plates can be formed of continuous frame plates extending around the perimeter of the stator core 210 or of separate sectors positioned symmetrically along the perimeter of the stator core 210. The frame plates in each sector are then attached to each other with axially X-X along an outer perimeter of the frame plates extending connection parts. The connection part and the frame plates in a sector form a frame plate package.
The axial X-X ends of the frame plate packages may be attached to a respective end plate with fastening means e.g. with bolts and nuts. The inner perimeter of the transverse cross section of the stator frame 220 may be of a circular form. The outer perimeter of the transverse cross section of the stator frame 220 may be of any form e.g. of a polygonal form.
The stator core 210 and the stator frame 220 can thus be manufactured independently simultaneously. The annular sheets of the stator core 210 are assembled to form the complete stator core 210 and then the stator winding 21 1 is wound into the slots 212 in the stator core 210. The stator frame is assembled from the end plates and the frame plates to form the complete stator frame 220. The stator core 210 is then attached to the stator frame 220. This can be done e.g. by L-shaped brackets. One branch of the brackets may be fastened with compression joints to the back beams 213 and the other branch may be fastened with compression joints to the frame plates. The compression joints in both branches can be achieved e.g. with bolts and nuts. Another possibility would be to use C-clamps on the back beams 213 and to attach the C-clamps by welding to the back beams 213 and the frame plates.
The synchronous machine 400 comprises further a connection space 250 within the synchronous machine 400. The connection space 250 may be formed as a separate box attached to the stator frame 220 or as an integral part of the stator frame 220. The stator winding 21 1 is connected to output terminals in the connection space 250.
The synchronous machine 400 comprises further an automatic voltage regulator (AVR) 500 for regulating the voltage of the synchronous machine 400.
Fig. 3 shows a cross section of one pole in the rotor and the corresponding portion of the stator in the synchronous machine. A single phase harmonics exciter winding 1 16 is shown in the figure. The number of exciter winding slots 1 17 is advantageously in the range of 1 .8 to 2.2 times, advantageously 2 times the number of stator winding slots 212 in a given sector for a single phase energy harvesting exciter winding 1 16. This means in other words that the pitch of the exciter winding slots 212 is in the range of 1 .8 to 2.2 times, advantageously 2 times denser than the pitch of the stator winding slots 212. The exciter winding 1 16 is formed of axially extending damper bars positioned in the outer surface of the pole shoe 1 13 adjacent to the air gap G1 between the rotor 100 and the stator 200. The exciter winding 1 16 in the rotor 100 has been designed to receive excitation from the stator winding 21 1 . AC harmonics frequencies above the nominal frequency of the synchronous machine are injected into the stator winding 21 1 so that said harmonics frequencies induce an AC current to the exciter winding 1 16 in the rotor 100 of the synchronous machine. The exciter winding 1 16 in the rotor 100 is designed to be compatible with the stator winding 21 1 at the injected harmonics frequencies. The idea is that only the injected harmonics frequencies in the stator winding 21 1 induce an AC current in the exciter winding 1 16.
The plurality of exciter windings 1 16 may be disposed within the pole 1 12, 1 13 of the rotor 100 at the radial outer edge of the shoe 1 13 of the pole 1 12, 1 13. The rotor 100 is a salient pole rotor, having field windings 1 1 1 disposed inwardly relative to the pole shoe 1 13 around the pole body 1 12. The harmonics exciter winding 1 16 is spaced every 180 electrical degrees. The exciter windings 1 16 can be disposed in slots 1 17 that are open towards the air gap G1 . The slots 1 17 can include only exciter windings 1 16 or the slots 1 17 could also include the field winding 1 1 1 , damper bars, or other auxiliary windings. Additional slots can be included on the pole shoe 1 13 that contain exciter windings 1 16 in addition to damper bars or other windings.
Figure 4 shows a DC power supply that can be used in the rotor of the synchronous machine. The high frequency voltage induced from the stator winding 21 1 into the exciter winding 1 16 of the rotor 100 can be fed to a DC power supply 150 positioned on the rotor 100 of the synchronous machine 400. The power supply 150 comprises a passive rectifier RB1 . The alternating current AC1 , AC2, AC3, AC4 from the exciter winding 1 16 of the rotor 100 is fed to the input of the power supply 150. The rectifier RB1 can be a multiphase passive rectifier including a full-wave diode bridge. The rectifier RB1 converts the alternating current AC1 , AC2, AC3, AC4 at the input of the rectifier RB1 to a direct current DC1 at the output of the rectifier RB1 . The injected harmonics have a higher frequency than the fundamental frequency of the synchronous machine, which means that fast switching diodes are preferred in the rectifier RB1 over conventional thyristors. However, new high frequency switching thyristors could be implemented in the power supply 150. A rectifier RB1 based on a full wave diode bridge includes four fast switching diodes. The power supply 150 supplies a controlled direct current DC1 from the output of the power supply 150 to the field windings 1 1 1 of the rotor 100. The DC power supply 150 is a passive power supply i.e. there is no need to be able to control the DC power supply 150.
Figure 5 shows a first embodiment of the invention. The stator winding 21 1 of the synchronous machine 400 is connected directly to the power grid 600. The automatic voltage regulator (AVR) 500 is connected to the stator winding 21 1 so that the AVR 500 receives measurement data of the electrical conditions at the terminals of the stator winding 21 1 . The AVR 500 can, based on the measurement data, determine the current that is required in the rotor windings 1 1 1 in order to generate the desired field in the air gap G1 . A harmonics injector 710 is connected via a current transformer 720 to the zero point or the star point of the stator winding 21 1 . The harmonics injector 710 is configured to inject harmonics into the stator winding 21 1 . The AVR 500 can indirectly control the current of the rotor windings 1 1 1 by controlling the harmonics injector 710 and thereby the injection of harmonics to the stator winding 21 1 . The injection of harmonics into the stator winding 21 1 will induce an alternating current AC1 in the exciter winding 1 16 and the alternating current AC1 in the exciter winding 1 16 will be rectified by the rectifier RB1 into a direct current DC1 which is then fed into the rotor winding 1 1 1 .
Figure 6 shows a second embodiment of the invention. A voltage transformer 730 is used instead of the current transformer in this embodiment. The voltage transformer connects the harmonics injector 710 to the zero point or star point of the stator winding 21 1 . The harmonics injector 710 is connect to the primary side of the voltage transformer 730 and the secondary side of the voltage transformer 730 is connected to the zero point of the stator winding 21 1 .
A frequency converter can be used as the harmonics injector 710 in the invention. The frequency converter 710 can be configured to inject harmonics into the stator winding 21 1 . The AVR 500 will control the harmonics injector 710 and thereby the injection of harmonics into the stator winding 21 1 . The frequency of the harmonics distortion could be kept constant, whereby the amplitude of the harmonics distortion could be regulated so that the desired excitation current in the rotor winding 1 1 1 is achieved at each time.
A current transformer 720 can be used when the current of the harmonics distortion is the quantity to be regulated. A voltage transformer 730 can be used when the voltage of the harmonics distortion is the quantity to be regulated. The frequency of the injected harmonics should be selected so that it induces well into the exciter winding 1 16. Harmonics in an air gap of an open slot type line fed synchronous machine mainly contain slotting harmonics due to the large slot openings in the stator. Some of the slotting harmonics are normally significantly larger compared to the other slotting harmonics in the air gap. When the slotting harmonics are utilized the width of the exciter winding slots 1 17 should be about the same as the width of the stator winding slots 212. If some lower frequencies e.g. the 5th order harmonics are utilized, then the width of the exciter winding slots 1 17 should be greater than the width of the stator winding slots 212.
It is advantageous to dimension the exciter winding slots 1 17 so that the pitch of the exciter winding slots 1 17 is in the range of 1 .8 to 2.2 times, more advantageously 2 times denser than the pitch of the stator winding slots 212. This will result in that the slot harmonics of the stator 200 can be utilized to their full extent. It is also advantageous to use the same slot harmonics frequency as the supply frequency in the harmonics injector 710. This will result in that the injected harmonics will be transferred effectively from the stator winding to the exciter winding in the rotor. The magnetic energy induced into the exciter winding can be regulated i.e. increased or decreased by regulating the phase angle and the amplitude of the injected harmonics.
It is possible also to use other frequencies than the slot harmonics in the harmonics injector 710. One could use e.g. a frequency that is half of the slot harmonics frequency in the harmonics injector 710. This would result in that the pitch of the rotor slots have to be doubled. The disadvantage would be that the "static" slot harmonics would be lost.
The transformer 720, 730 provides galvanic isolation between the stator winding 21 1 and the harmonics injector 710.
The invention can be used in a synchronous machine having a star connected or delta connected stator winding. The invention is not limited to a salient pole synchronous machine as disclosed in the figures, but can be used in any synchronous machine.
It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A synchronous machine, characterized in that it comprises:
a stator (200) comprising a stator winding (21 1 ),
a rotating rotor (100) comprising a rotor winding (1 1 1 ) and an exciter winding (1 16) disposed adjacent to an air gap (G1 ) formed between the stator (200) and the rotor (100),
a DC power supply (150) comprising a rectifier (RB1 ) positioned on the rotor (100), the exciter winding (1 16) being electrically coupled to an input of the DC power supply (150) and an output of the DC power supply (150) being electrically coupled to the rotor winding (1 1 1 ),
a voltage regulator (500) electrically coupled to the stator winding
(21 1 ),
a harmonics injector (710) connected via a transformer (720, 730) to a zero point of the stator winding (21 1 ), whereby the harmonics injector (710) is controlled by the voltage regulator (500) to inject a harmonics distortion into the stator winding (21 1 ), said harmonics distortion being induced from the stator winding (21 1 ) to the exciter winding (1 16) in the rotor (100) and thereby to the input of the DC power supply (150), said harmonics distortion being rectified in the rectifier (RB1 ) of the DC power supply (150) and supplied as DC current to the stator winding (1 1 1 ) from the output of the DC power supply (150).
2. A synchronous machine according to claim 1 , characterized in that the stator winding (21 1 ) is connected directly to the power grid.
3. A synchronous machine according to claim 1 or 2, characterized in that the harmonics injector (710) is a frequency converter.
4. A synchronous machine according to any one of claims 1 to 3, characterized in that the transformer (720, 730) is a current transformer (720).
5. A synchronous machine according to any one of claims 1 to 3, characterized in that the transformer (720, 730) is a voltage transformer (730).
6. A synchronous machine according to any one of claims 1 to 5, characterized in that the pitch of the exciter winding slots (1 17) is in the range of 1 .8 to 2.2 times denser than the pitch of the stator winding slots (212).
7. A method for operating a synchronous machine, characterized by the steps of:
measuring the electrical conditions in a stator winding (21 1 ) of the synchronous machine with a voltage regulator (500),
selecting a predetermined current level in a rotor winding (1 1 1 ) of the synchronous machine based on the measured electrical conditions in the stator winding (21 1 ) of the synchronous machine,
injecting a harmonics distortion to the stator winding (21 1 ) of the synchronous machine with a harmonics distortion injector (710) connected via a transformer (720, 730) to a zero point of a stator winding (21 1 ) of the synchronous machine based on the predetermined current level in the rotor winding (1 1 1 ) of the synchronous machine, whereby a current attributable to the harmonics distortion is induced in an exciter winding (1 16) disposed in a rotor (100) of the synchronous machine adjacent to an air gap (G1 ) formed between the rotor (100) and the stator (200) of the synchronous machine,
rectifying the current in the exciter winding (1 16), and
supplying the rectified current to the rotor winding (1 1 1 ), thereby effecting the predetermined current level in the rotor winding (1 1 1 ).
PCT/EP2015/068639 2015-08-13 2015-08-13 A synchronous machine and a method for operating the machine WO2017025142A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019134784A1 (en) 2018-01-04 2019-07-11 Abb Schweiz Ag Exciterless synchronous machine with damper bars
WO2023117242A1 (en) * 2021-12-20 2023-06-29 Robert Bosch Gmbh Inductive transformer system for transmitting electrical energy into an excitation winding of a rotor

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GB2071430A (en) * 1980-02-21 1981-09-16 Dobson Pag Eng Ltd Brushless A.C. Generators
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JP2939914B2 (en) * 1991-03-11 1999-08-25 新ダイワ工業株式会社 Brushless self-excited synchronous generator
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019134784A1 (en) 2018-01-04 2019-07-11 Abb Schweiz Ag Exciterless synchronous machine with damper bars
WO2023117242A1 (en) * 2021-12-20 2023-06-29 Robert Bosch Gmbh Inductive transformer system for transmitting electrical energy into an excitation winding of a rotor

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