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Title:
EXCITERLESS SYNCHRONOUS MACHINE WITH DAMPER BARS
Document Type and Number:
WIPO Patent Application WO/2019/134784
Kind Code:
A1
Abstract:
The present disclosure relates to an exciterless synchronous machine (1) comprising: a stator (3) provided with a plurality of stator slots (3a), a rotor (5) comprising a field winding (5b) and a plurality of poles (5a), each having a pole shoe (5c), a power converter, wherein the stator (3) and the rotor (5) are arranged with an air gap (G) between them, each pole shoe (5c) having a plurality of rotor slots (5d) and an excitation coil (51) arranged in the rotor slots (5d), wherein the power converter is connected between the excitation coils (5f) and the field winding (5b), and wherein each pole (5a) comprises at least one damper bar (7a, 7b) arranged interiorly in the pole (5a), each damper bar (7a, 7b) being at least at a gap distance z from the air gap (G), the gap distance z being greater than a rotor slot depth 1 of at least one of the rotor slots (5d).

Inventors:
RODRIGUEZ, Pedro (Gideonsbergsgatan 10A, Västerås, 722 25, SE)
PATHMANATHAN, Mehanathan (Norra Ringvägen 20A, Västerås, 722 15, SE)
LIN, Chenjie (2617 Perthshire Ln, Fuquay Varina, North Carolina, 27526, US)
GHANSHYAM, Shrestha (1725 Fairbanks Road, Cary, North Carolina, 27513, US)
Application Number:
EP2018/083999
Publication Date:
July 11, 2019
Filing Date:
December 07, 2018
Export Citation:
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Assignee:
ABB SCHWEIZ AG (Brown Boveri Strasse 6, 5400 Baden, 5400, CH)
International Classes:
H02K9/12; H02K9/28; H02K11/042; H02P9/30
Domestic Patent References:
WO2017025142A12017-02-16
WO2017025142A12017-02-16
Foreign References:
US20160211787A12016-07-21
DE102010060998A12012-06-06
CN201263113Y2009-06-24
CN1545202A2004-11-10
Attorney, Agent or Firm:
SAVELA, Reino (ABB AB, Intellectual PropertyForskargränd 7, Västerås, 721 78, SE)
Download PDF:
Claims:
CLAIMS

1. An exciterless synchronous machine (l) comprising: a stator (3) provided with a plurality of stator slots (3a), a rotor (5) comprising a field winding (5b) and a plurality of poles (5a), each having a pole shoe (5c), a power converter, wherein the stator (3) and the rotor (5) are arranged with an air gap (G) between them, each pole shoe (5c) having a plurality of rotor slots (sd) and an excitation coil (sf) arranged in the rotor slots (sd), and wherein the power converter is connected between the excitation coils (5f) and the field winding (5b), characterized in that each pole (5a) comprises at least one damper bar (7a, 7b) arranged interiorly in the pole (5a), each damper bar (7a, 7b) being at least at a gap distance (z) from the air gap (G), the gap distance (z) being greater than a rotor slot depth (1) of at least one of the rotor slots (sd).

2. The exciterless synchronous machine (1) as claimed in claim 1, wherein adjacent stator slots (3a) are arranged at a stator slot distance (D), and the damper bars (7a, 7b) of a pole (5a) are arranged at a damper bar distance (L) from each other, the damper bar distance (L) being at least four times the stator slot distance (D).

3. The exciterless synchronous machine (1) as claimed in claim 2, wherein the damper bar distance (L) is more than four times the stator slot distance (D). 4. The exciterless synchronous machine (1) as claimed in claim 2 or 3, wherein adjacent rotor slots (sd) in a pole shoe (5c) are arranged at a rotor slot distance (d), wherein the rotor slot distance (d) is half the stator slot distance (D).

5. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein the gap distance (z) is at least twice the rotor slot depth (1) of at least one of the rotor slots (sd).

6. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein the gap distance (z) is greater than a rotor slot depth (1) of the deepest rotor slot (sd).

7. The exciterless synchronous machine (1) as claimed in claim 6, wherein the gap distance (z) is at least twice the rotor slot depth (1) of the deepest rotor slot (sd).

8. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein each pole (5a) comprises at least two damper bars (7a, 7b).

9. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein each damper bar (7a, 7b) at least partially overlaps at least one of the rotor slots (sd) in the same pole (5a) in a radial direction in relation to the rotational axis of the rotor.

10. The exciterless synchronous machine (1) as claimed in claim 9, wherein each damper bar 7a, 7b is aligned with a rotor slot 5d in the same pole 5a in the radial direction.

11. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein each damper bar (7a, 7b) is arranged at the same gap distance (z).

12. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein each pole (5a) has at least one bore extending in the axial direction of the rotor (5), wherein each damper bar (7a, 7b) is arranged in a respective bore.

13. The exciterless synchronous machine (1) as claimed in any of the preceding claims, wherein the exciterless synchronous machine (1) is a motor.

Description:
EXCITERLESS SYNCHRONOUS MACHINE WITH DAMPER BARS

TECHNICAL FIELD

The present disclosure generally relates to synchronous machines and in particular to exciterless synchronous machines.

BACKGROUND

Synchronous machine excitation systems are designed to supply the required field current to the rotor winding or field winding of a synchronous machine. A difficult part of the excitation process is the mechanical interface which supplies this current to the rotating field winding. This is usually done through carbon brushes (static excitation) or using an exciter machine with a rotating diode or thyristor rectifier (brushless excitation).

The main machine used in static, and brushless -excitation methods commonly uses damper bars in the surface of the rotor poles. These bars are short-circuited conductors which often have inter-pole connections. Damper bars perform a number of key roles in the main machine, such as allowing direct-on-line starting of synchronous motors, because of torque production due to induced currents in damper bars, and damps the fluctuation in rotational speed due to rotating loads with pulsating torque. The exciterless concept uses excitation coils in the surface of the rotor poles which are positioned to harvest the magnetic energy of the slotting harmonic. A power electronic converter is used to convert this harvested energy into controllable DC current which is supplied to the field winding.

One problem with typical exciterless machines is that they do not enable on- line starting and transient damping. US2016/0211787 At discloses an exciterless synchronous machine in which damper bars can be implemented in addition to the exciter windings. It is also disclosed that the exciter windings may be shorted so that they operate as traditional damper bars. W Ό2017025142 discloses a synchronous machine which comprises exciter windings that are designed to receive excitation from the stator winding. AC harmonic frequencies above the nominal frequency of the synchronous machine are injected into the stator winding so that the harmonic frequencies induce an AC current to the exciter winding. The exciter winding is formed of axially extending damper bars positioned in the outer surface of the pole shoe. It is also disclosed that the slots for the exciter windings can include also damper bars.

One problem with the above configurations is that they will not provide enough damping for certain applications. Moreover, on-line start-up and transient damping may therefore not be provided as required. For example, for some motor applications the machine may suddenly be under a step torque variation. In such cases, existing damping solutions for an exciterless synchronous machine are not sufficient.

SUMMARY

In view of the above, an object of the present disclosure is to provide an exciterless synchronous machine which solves, or at least mitigates, the problems of the prior art.

There is hence according to a first aspect of the present disclosure provided an exciterless synchronous machine comprising: a stator provided with a plurality of stator slots, a rotor comprising a field winding and a plurality of poles, each having a pole shoe, a power converter, wherein the stator and the rotor are arranged with an air gap between them, each pole shoe having a plurality of rotor slots and an excitation coil arranged in the rotor slots, wherein the power converter is connected between the excitation coils and the field winding, and wherein each pole comprises at least one damper bar arranged interiorly in the pole, each damper bar being at least at a gap distance from the air gap, the gap distance being greater than a rotor slot depth of at least one of the rotor slots. The gap distance is determined as a radial distance from a mass centre of a cross section of each damper bar to the air gap. The radial distance is radial in relation to the rotational axis of the rotor, and the cross section is taken along a plane perpendicular to the rotational axis of the rotor.

Due to the location of the damper bars at least partially below the respective excitation coils, efficient damping may be provided in the event of transients. Moreover, the synchronous machine will also be able to self-start.

Additionally, due to the position of the damping bars, the energy harvested by the excitation coils can be increased. This is because the damper cage formed by the damper bars damp the harmonics of the main magnetomotive force. There is hence a synergistic effect between the excitation coils and the damper bars.

Additionally, due to the internal location of the damper bars in the poles, the damper bars are less likely to fail. The centrifugal forces acting on the damper bars is also lower, since they are located closer to the central axis of the rotor.

The damper bars form a damper cage. The damper cage is buried below the outer surface of the pole shoes.

There is at least one damper bar provided in each pole. There may be more than one damper bars in a pole, in particular an odd number or an even number greater than one. Generally, the more the damper bars the better is the damping.

It has been shown that the total losses of the present exciterless synchronous machine are at the same level as of a conventional exciterless synchronous machine. However, since the present exciterless synchronous machine with the buried damper cage allows to harvest more energy for the excitation, the total efficiency for the present exciterless synchronous machine is better than for the conventional one.

The exciterless synchronous machine with the buried damper cage thus improves the machine performance besides adding damping effect. Location and resistance of the cage is a trade-off between damping, losses and practicality of cage installation. The machine could be even able to start-up asynchronously.

The damper bars may be short-circuited at all times.

The gap distance may be greater than the rotor slot depth of any of the rotor slots.

According to one embodiment adjacent stator slots are arranged at a stator slot distance, and the damper bars of a pole are arranged at a damper bar distance from each other, the damper bar distance being at least four times the stator slot distance.

The stator slot distance is determined as an angular distance centre-to-centre between adjacent stator slots measured from the rotational axis of the rotor in a plane perpendicular to the same.

The damper bar distance is determined as an angular distance centre-to- centre between two adjacent damper bars of a pole measured from the rotational axis of the rotor in a plane perpendicular to the same.

According to one embodiment the damper bar distance is more than four times the stator slot distance.

According to one embodiment adjacent rotor slots in a pole shoe are arranged at a rotor slot distance, wherein the rotor slot distance is half the stator slot distance.

The rotor slot distance is determined as an angular distance centre-to-centre between adjacent rotor slots measured from the rotational axis of the rotor in a plane perpendicular to the same.

According to one embodiment the gap distance is at least twice the rotor slot depth of at least one of the rotor slots. According to one embodiment the gap distance is at least twice the rotor slot depth of the deepest rotor slot.

According to one embodiment the gap distance is more than twice the rotor slot depth of at least one of the rotor slots

According to one embodiment the gap distance is more than twice the rotor slot depth of the deepest rotor slot.

According to one embodiment each damper bar at least partially overlaps at least one of the rotor slots in the same pole in a radial direction in relation to the rotational axis of the rotor.

According to one embodiment each damper bar is aligned with a rotor slot in the same pole in the radial direction.

According to one embodiment each damper bar is arranged at the same gap distance.

According to one embodiment each pole has at least one bore extending in the axial direction of the rotor, wherein each damper bar is arranged in a respective bore.

According to one embodiment the exciterless synchronous machine is a motor. Alternatively, the synchronous machine may be a generator.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. l shows an example of a cross-section of a portion of a synchronous machine;

Fig. 2 shows a close-up of the view depicted in Fig. l; and

Figs 3a and 3b show extracted power of an exciterless synchronous machine comprising damper bars as disclosed herein and of a conventional exciterless synchronous machine, respectively.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying

embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig. 1 shows a cross-sectional view of a portion of a synchronous machine 1. The exemplified synchronous machine 1 is a rotating type of synchronous machine. The synchronous machine 1 comprises a stator 3 and a rotor 5. The stator 3 is configured to receive the rotor 5. The rotor 5 is configured to rotate relative to the stator 3. Alternatively, the inverse configuration is also possible, where the rotor is arranged around the stator, a so-called outer rotor machine.

The stator 3 is provided with a plurality of stator slots 3a. In particular, the stator 3 has an inner perimeter surface 3b which faces the rotor 5 and the inner perimeter surface 3b is provided with the stator slots 3a. The stator 3 further comprises one or more stator windings 3c arranged in the stator slots 3a.

The rotor 5 comprises a plurality of poles 5a. In Fig. 1, only one pole is shown. Any two poles arranged along the same radial axis form a pole pair. Each pole pair forms part of an electromagnet. Each pole 5a comprises a pole shoe 5c.

In particular, the radially outermost portion of each pole 5a is the pole shoe 5c. Each pole shoe 5c is provided with a plurality of rotor slots 5d arranged one after the other in the circumferential direction, along an external surface 5e of the pole shoe 5c. The external surface 5e faces the inner perimeter surface 3b of the stator 3. The stator 3 and the rotor 5 are separated by an air gap G.

The rotor 5 furthermore comprises excitation coils sf. The excitation coils sf are provided in the rotor slots sd. For example, each pole pair may comprise a respective excitation coil sf arranged in the corresponding rotor slots ,¾d of the pole shoes 5c of the pole pair. The excitation coils sf are configured to harvest energy obtained from harmonics in the magnetic field from the stator winding(s) 3c.

The rotor 5 furthermore comprises a field winding 5b configured to electromagnetically interact with the stator winding(s) 3c. The field winding 5b is wound around the poles 5a.

The synchronous machine 1 also includes a power converter system (not shown) connected between the excitation coils sf and the field winding 5b. The power converter system may for example include a respective passive rectifier for each pole pair/excitation coil and a power converter in the form of a DC-DC converter common to all the pole pairs. Alternatively, the power converter system may include power converter in the form of an AC-DC converter which is common for all of the pole pairs and excitation coils sf. In this latter case, no rectifiers are necessary. The power converter system hence converts AC currents from the excitation coils sf as obtained by energy harvesting to a controlled DC current fed to the field winding 5b.

The synchronous machine 1 furthermore comprises damper bars 7a and 7b. Each pole 5a comprises two damper bars 7a and 7b. The poles 5a may be provided with a bore, opening, or channel distanced from the external surface 5e and extending in the interior of the pole 5a. The bore extends in an axial direction of the rotor 5, i.e. in the length direction of the rotor 5. The damper bars 7a and 7b are arranged in respective bores. The damper bars 7a and 7b hence extend in the interior of the pole 5a. The bores and thus the damper bars 7a and 7b are arranged at a greater distance from the external surface 5e of the pole shoe 5c than the rotor slots 5d and the excitation coil 5f.

The damper bars 7a and 7b may be arranged radially inwards of the rotor slots 5d of the pole 5a in question.

The damper bars 7a and 7b may be constantly short-circuited.

Fig. 2 shows a close-up view of the configuration shown in Fig. 1. The close- up view shows a preferable configuration of the damper bars 7a and 7b. The stator slots 3a are located at a stator slot distance D from each other. Each pair of adjacent stator slots 3a may have the same stator slot distance D between them. The rotor slots ,¾d are located at a rotor slot distance d from each other. Each pair of adjacent rotor slot sd may have the same rotor slot distance d between them. The rotor slot distance d is preferably equal to half the stator slot distance, i.e. d=D/2.

The rotor slots ,¾d form recesses or grooves in the external surface se of the pole shoe 5c. The rotor slots sd have a rotor slot depth 1. The rotor slot depth 1 may vary depending on the location of the rotor slot along the pole shoe 5c. The rotor slot depth 1 is the distance from the air gap G or the mouth of the rotor slot sd to the bottom of the rotor slot sd.

Each damper bar 7a, 7b may at least partially overlap at least one rotor slot 5d in the same pole 5a in a radial direction in relation to the rotational axis of the rotor. That is, for each damper bar 7a, 7b it may be possible to draw, in the radial direction, at least one straight line that crosses the respective damper bar 7a, 7b and a rotor slot sd in the same pole 5a. Each damper bar 7a, 7b may be aligned with a rotor slot sd in the same pole 5a in the radial direction. That is, for each damper bar 7a, 7b it may be possible to draw, in the radial direction, a straight line that crosses the mass centre of the damper bar’s 7a, 7b cross section and a mass centre of the respective rotor slot’s sd cross section. The two damper bars 7a, 7b may be arranged symmetrically in the pole 5 a.

Each damper bar 7a and 7b may be arranged at a gap distance z from the air gap G. The gap distance z is at least two times the rotor slot depth 1, i.e. z>2l. Preferably, the gap distance z is more than twice the rotor slot depth 1, i.e.

Z>2l.

The damper bars 7a and 7b may be arranged at a damper bar distance L from each other. The damper bar distance L is at least four times the stator slot distance D, i.e. L>4D. Preferably, the damper bar distance L is more than four times the stator slot distance D, i.e. L>4D.

Fig. 3a shows a graph of extracted power of a two-phase exciterless synchronous machine including interior damper bars 7a and 7b as disclosed herein and with a 5 mm air gap G. Fig. 3b shows a graph of extracted power of a conventional two-phase exciterless synchronous machine with a 5 mm air gap. It can be seen that about 10% more power can be extracted via the excitation coils when the exciterless synchronous machine includes a damper cage as disclosed herein.

The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.