Rotor for a synchronous electric machine

Abstract

The present disclosure relates to a rotor for a synchronous electric machine. A rotor (5) for a synchronous electric machine (1), the rotor comprising a rotor core (7) having a longitudinal center axis (A), and a plurality of salient poles (9), each comprising a solid metal pole shoe (11) mounted to the rotor core (7) and forming a radially outermost portion of the respective salient pole (9), wherein each pole shoe (11) has a pole shoe body (13) provided with a longitudinal slit (17) extending mainly in a direction parallel to the longitudinal center axis (A), each pole shoe (11) comprising a metal strip (19) arranged in the slit (17), wherein each metal strip (19) comprises or consists of an electrically conductive non-ferromagnetic material, and wherein the electrically conductive non-ferromagnetic material has a lower DC resistivity than the pole shoe body (13).

Description

Technical Field

[0001] This disclosure generally relates to rotors of synchronous motors, synchronous motors, and motor systems including synchronous motors driven by load-commutated inverters (LCIs). Background Technology

[0002] LCI operation in medium-voltage solid salient pole synchronous motors causes significant losses on the rotor surface, which are difficult to cool effectively. This results in localized temperature rises known as hot spots. Hot spot temperatures on the rotor surface are often the design limits for such machines today. This applies to motors designed for safe areas, but is even more critical in hazardous areas, particularly Zone 1 hazardous areas. If hot spots are not controlled during the motor design phase, the worst-case scenario could be gas ignition. For machines in safe areas, the focus is typically not on the hot spot itself, but on heat transfer from the hot spot to the field winding insulation. High temperatures in the field winding insulation shorten the motor's expected lifespan. Overall, the output power of a given LCI drive motor is currently limited by the losses occurring on the rotor pole shoe surface. Summary of the Invention

[0003] It can be noted that, compared to solid salient-pole synchronous motors driven by LCI, laminated rotor machines, i.e., machines with rotors formed of laminated metal sheets, can have damping windings mounted on the outer periphery of the rotor. In this case, high-frequency losses ultimately enter this winding. In solid metal pole shoe machines driven by LCI, the damping effect is "built into" the rotor structure by allowing eddy currents to flow freely within the rotor. Unfortunately, high-frequency currents flow in a very thin skin layer on the rotor surface, resulting in very high effective resistance and thus significant losses.

[0004] In view of the above, the purpose of this disclosure is to provide a rotor for a synchronous motor that solves or at least alleviates the problems of the prior art.

[0005] Therefore, according to a first aspect of this disclosure, a rotor for a synchronous motor is provided, the rotor comprising: a rotor core having a longitudinal central axis; and a plurality of salient poles, each salient pole including a pole shoe mounted to the rotor core and forming the radially outermost portion of the respective salient pole, wherein each pole shoe has a pole shoe body having a longitudinal slit provided therein, the longitudinal slit extending primarily in a direction parallel to the longitudinal central axis, each pole shoe including a metal strip arranged in the slit, wherein each metal strip includes or is composed of a conductive non-ferromagnetic material, the conductive non-ferromagnetic material partially forming the radially outermost surface of the pole shoe, and wherein the conductive non-ferromagnetic material has a lower DC resistivity than the pole shoe body.

[0006] The losses that would otherwise occur on the outermost radial surface can therefore be greatly reduced. As a result, the output power of the synchronous motor, including the rotor and driven by the LCI, can be increased.

[0007] The DC resistivity of conductive non-ferromagnetic materials at 150°C is lower than that of the pole piece body.

[0008] According to one embodiment, for each salient pole, the slit is arranged to deviate from a plane of symmetry in the circumferential direction of the rotor core, the plane of symmetry including the longitudinal central axis and the longitudinal centerline of the corresponding salient pole.

[0009] The hotspots are arranged circumferentially off-plane. The location of the hotspots depends on whether the synchronous motor driven by the LCI operates as a motor or a generator.

[0010] When an LCI-driven synchronous motor, including the rotor of the first aspect, is to be operated as a motor, the metal strip of each pole shoe is arranged such that it is located on the lagging side of the pole shoe during the rotation of the rotor core. This is advantageous because when the LCI-driven synchronous motor is to be operated as a motor, hot spots always appear on the lagging side of the pole shoe.

[0011] When an LCI-driven synchronous motor, including the rotor of the first aspect, is to be operated as a generator, the metal strip of each pole shoe is arranged such that it is located on the leading side of the pole shoe during the rotation of the rotor core. This is advantageous because when the LCI-driven synchronous motor is to be operated as a generator, the hot spot always appears on the leading side of the pole shoe.

[0012] According to one embodiment, the conductive non-ferromagnetic material has a lower DC resistivity than iron.

[0013] According to one embodiment, the conductive non-ferromagnetic material is copper or a copper alloy.

[0014] According to one embodiment, each pole shoe body is made of a single piece of steel.

[0015] According to one embodiment, each metal strip includes a base on which a conductive non-ferromagnetic material is disposed radially inside the conductive non-ferromagnetic material.

[0016] According to one embodiment, a conductive non-ferromagnetic material is bonded to the base.

[0017] The combination can be a mechanical combination using, for example, bolts; it can be chemical, through thermal fusion such as welding, brazing or brazing; or thermo-solid combination such as friction stir welding; or through crimping.

[0018] In one example, the metal strip may be composed of a conductive, non-ferromagnetic material, which may be cast or sintered in the slit. In another example, the conductive, non-ferromagnetic material may be cast or sintered onto the base.

[0019] According to one embodiment, each base is made of the same material as the pole piece body. This minimizes the amount of conductive non-ferromagnetic material required and reduces the mechanical strength requirements of the conductive non-ferromagnetic material. It also allows for better control of manufacturing to minimize unwanted heating or other problems associated with thermal bonding of dissimilar materials. Furthermore, it reduces concerns about thermal expansion mismatch between the metal strip and the pole piece body.

[0020] According to one embodiment, each base is interlocked with the corresponding pole shoe body in the radial direction.

[0021] According to one embodiment, each pole piece has a central section located between a first axial end and a second axial end of the pole piece, wherein a conductive non-ferromagnetic material in the slit extends along the central section.

[0022] According to one embodiment, each pole shoe body includes a single slit.

[0023] According to a second aspect of this disclosure, a synchronous motor is provided, the synchronous motor including the rotor of the first aspect.

[0024] According to a third aspect of this disclosure, a motor system is provided, comprising: a synchronous motor of the second aspect, and an LCI configured to drive the synchronous motor.

[0025] According to one embodiment, the LCI is an N-pulse LCI, where N is a positive integer multiple of 6, and where the radial thickness of the conductive non-ferromagnetic material is at least half the skin depth of the maximum loss harmonic of the N-pulse LCI, which causes the maximum loss on the rotor at a temperature of 150°C at the lowest frequency of occurrence of the LCI and the synchronous motor during normal operation.

[0026] 150°C is the typical operating temperature reached when an LCI-driven synchronous motor is in operation.

[0027] In one example, the radial thickness of the conductive non-ferromagnetic material is at least 2 / 3, 3 / 4, or one skin depth of the maximum loss harmonic of the N-pulse LCI, which causes the maximum loss on the rotor at the lowest frequency of occurrence during normal operation of the LCI and the synchronous motor, at a temperature of 150°C.

[0028] According to one embodiment, the conductive non-ferromagnetic material provides a greater skin depth for the maximum loss harmonic than the pole piece body.

[0029] According to one embodiment, the synchronous motor has a rated power of at least 20 MW. The synchronous motor may, for example, be rated at at least 30 MW.

[0030] Synchronous motors can be medium-voltage synchronous motors. Therefore, the rated voltage of a synchronous motor driven by an LCI can be in the range of 1 kV to 30 kV, such as 1 kV to 15 kV.

[0031] Synchronous motors can be operated as either motors or generators.

[0032] Generally, all terms used in the claims shall be interpreted according to their ordinary meaning in the technical field, unless otherwise expressly defined herein. Unless otherwise expressly stated, all references to “a”, “an”, “element”, “device”, “component”, “apparatus”, etc. shall be publicly interpreted as referring to at least one instance of that element, device, component, apparatus, etc. Attached Figure Description

[0033] Specific embodiments of the concept of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 The longitudinal section of the synchronous motor connected to the LCI is shown schematically;

[0035] Figure 2 It shows Figure 1 A perspective view of an example rotor of a synchronous motor;

[0036] Figure 3 It is the cross-section of the rotor;

[0037] Figures 4 to 5 Each shows an example of a single salient pole of the rotor; and

[0038] Figure 6 It is the longitudinal section of the pole shoe before it is installed onto the rotor core. Detailed Implementation

[0039] The concept of the invention will now be described more fully below with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the concept of the invention may 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 concept of the invention to those skilled in the art. Throughout this specification, the same reference numerals refer to the same elements.

[0040] Figure 1 A longitudinal section of an example of synchronous motor 1 is schematically shown. Figure 1Also shown is LCI 4, which is configured to drive synchronous motor 1. Synchronous motor 1 and LCI 4 form motor system 2.

[0041] The synchronous motor 1 includes a stator 3.

[0042] The synchronous motor 1 includes a rotor 5.

[0043] The rotor 5 is rotatably arranged in the stator 3.

[0044] The rotor 5 is arranged to interact electromagnetically with the stator 3.

[0045] Rotor 5 includes rotor core 7.

[0046] The rotor 5 also includes a plurality of salient poles 9 which are attached to the rotor core 7.

[0047] LCI 4 is an N-pulse LCI, where N is a positive integer multiple of 6. LCI 4 can be, for example, a 6-pulse or a 12-pulse LCI.

[0048] Now go to Figure 2 An example of rotor 5 is shown in perspective view. This example shows rotor 5 as a 4-pole rotor, but it should be understood that rotor 5 can have any even number of salient poles 9, such as six or eight.

[0049] Each salient pole 9 includes a corresponding pole shoe 11, and each pole shoe 11 has a pole shoe body 13. The pole shoe body 13 is made of a single piece of metal (such as steel).

[0050] Each pole shoe 11 is mounted on the rotor core 7.

[0051] Each pole piece 11 forms the outermost radial portion of the corresponding salient pole 9.

[0052] Each pole piece 11 defines the radial outermost surface 15 of the corresponding salient pole 9.

[0053] Each pole shoe body 13 is provided with a longitudinal slit or groove 17, which extends primarily in a direction parallel to the longitudinal central axis A of the rotor core 7. The slits 17 can be arranged completely parallel to the longitudinal central axis A, or they can be arranged at an angle of up to 5° relative to the longitudinal central axis A. The slits 17 can have a constant width along their length, i.e., a constant dimension in the circumferential direction of the rotor 5, or the width can vary.

[0054] In addition, each pole piece 11 includes a metal strip 19 arranged in the slit 17. The metal strip 19 comprises or is composed of a conductive non-ferromagnetic material.

[0055] The conductive non-ferromagnetic material has a lower DC resistivity than the pole piece body 13. Therefore, the conductive non-ferromagnetic material has a lower DC resistivity than the material of the pole piece body 13. The DC resistivity is considered at 150°C.

[0056] Conductive non-ferromagnetic materials can be, for example, copper, such as pure copper or copper alloys.

[0057] A conductive, non-ferromagnetic material forms the outermost radial surface of the metal strip 19. Since the metal strip 19 is arranged in the slit 17, the conductive, non-ferromagnetic material is the outer surface of the pole piece 11.

[0058] The outer surface of the metal strip 19 may be flush with or level with the radial outermost surface 15 surrounding the metal strip 19.

[0059] For each salient pole 9, the slit 17 and the metal strip 19 are arranged circumferentially off-center from the plane of symmetry P of the rotor core 7, which includes the longitudinal central axis A of the rotor core 7 and the longitudinal centerline of the salient pole 9. Without conductive non-ferromagnetic material arranged in the slit 17, hot spots will appear circumferentially off-center from the plane of symmetry P. If the synchronous motor 1 is to be operated as a motor, the slit 17 is arranged on the circumferentially off-center lagging side, and if the synchronous motor 1 is to be operated as a generator, the slit 17 is arranged on the leading side. For a synchronous motor 1 that operates as both a motor and a generator, in some examples, each salient pole 9 may include two slits 17 with corresponding metal strips 19 arranged, each slit 17 being arranged circumferentially off-center from the corresponding side of the plane of symmetry P. If the synchronous motor 1 operates only as a motor or a generator, each salient pole 9 may include a single slit 17.

[0060] Each pole shoe 11 has a first axial end 11a and a second axial end 11b opposite to the first axial end 11a. The axial ends 11a and 11b are the longitudinal axial ends of the pole shoe 11.

[0061] Each pole piece 11 has a central section located between the first axial end 11a and the second axial end 11b. A slit 17 extends along the central section. A metal strip 19, and thus a conductive, non-ferromagnetic material, also extends along the central section.

[0062] If the synchronous motor 1 is symmetrically cooled, that is, if cooling is provided at the two axial ends 11a, 11b of the pole shoe 11, then the slit 17 can be axially symmetrically arranged in the longitudinal direction on the corresponding pole shoe 11.

[0063] If the synchronous motor 1 is asymmetrically cooled, that is, if cooling is provided only at one of the axial ends 11a, 11b of the pole shoe 11, the slit 17 can be arranged to be axially offset in the longitudinal direction relative to the center of the pole shoe 11, wherein the slit 17 is arranged closer to the axial end 11a, 11b that suffers poorer cooling.

[0064] In one example, the slit 17 and metal strip 19 of each pole shoe 11 can extend along the entire axial length of the pole shoe 11, that is, from the first axial end 11a to the second axial end 11b.

[0065] The radial thickness of the conductive non-ferromagnetic material can be at least half the skin depth of the maximum loss harmonic of the N-pulse LCI, which causes the maximum loss on the rotor at the lowest frequency of occurrence during normal operation of LCI 4 and synchronous motor 1, at a temperature of 150°C.

[0066] For example, if N=12, meaning LCI 4 is a 12-pulse LCI, and the fundamental frequency of LCI 4 is 50 Hz, then the frequency of the maximum loss harmonic that causes the maximum loss is 600 Hz. In this case, if the conductive non-ferromagnetic material is composed of pure copper, the skin depth at 150°C is 3.26 mm. This means that in this example, the radial thickness of the conductive non-ferromagnetic material is at least 1.63 mm. If the fundamental frequency of LCI 4 is 30 Hz (which can be the lowest frequency that occurs during the normal operation of LCI 4 and synchronous motor 1), then the skin depth for pure copper at 150°C is 4.2 mm. This means that in this example, the radial thickness of the conductive non-ferromagnetic material is at least 2.1 mm.

[0067] Generally, the skin depth δ of a conductive nonferromagnetic material is defined by the following equation (1):

[0068] in Let f be the resistivity of copper at 150℃, and f be the fundamental frequency. Let be the permeability in free space, and is the relative permeability of a conductive non-ferromagnetic material.

[0069] Compared to the pole piece body 13, the conductive non-ferromagnetic material provides a greater skin depth for the maximum loss harmonics discussed above. This is due to the material difference between the pole piece body 13 and the conductive non-ferromagnetic material.

[0070] The radial thickness of the conductive non-ferromagnetic material can be several times smaller than the width of the conductive non-ferromagnetic material. In one example, the width (i.e., the maximum dimension of the conductive non-ferromagnetic material in the circumferential direction of rotor 5) can be at least an order of magnitude (10 times) larger than the radial thickness.

[0071] The synchronous motor 1 includes a field winding 10, which is disposed on a salient pole 9 and located radially inside the pole shoe 11.

[0072] Metal strip 19 can have a variety of different configurations, see reference Figures 3 to 5 Examples of these configurations are provided.

[0073] Figure 3 The cross-section of rotor 5 at its axial position where the metal strip 19 is provided is schematically shown. According to this example, the metal strip 19 is composed of a conductive, non-ferromagnetic material. The metal strip 19 can be thermally bonded to the corresponding pole piece body 13, for example. Thermal bonding can be achieved, for example, by brazing, welding, or soldering the conductive, non-ferromagnetic material to the pole piece body 13.

[0074] exist Figure 4 In the example, the metal strip 19 interlocks with the slit 17 in the radial direction. The metal strip 19 can be anchored using the slit 17. For example, the slit 17 can have an inverted, inverted T-shaped, or dovetail shape in cross-section, and the metal strip 19 can have a corresponding T-shaped or dovetail cross-section. In this case, during manufacturing, the slit 17 can be opened from one end of the pole shoe body 13, allowing the metal strip 19 to be slid into the slit 17. This opening can then be closed, for example by bolting or otherwise attaching the metal strip 19 to one or both longitudinal axial ends arranged in the slit 17 to the end pieces of the pole shoe body 13, thereby axially locking the position of the metal strip 19.

[0075] Figure 5 Another example of a metal strip is shown. The metal strip 19' includes a base 21 on which a conductive non-ferromagnetic material 23 is disposed. The base 21 is disposed radially inside the conductive non-ferromagnetic material 23. The base 21 may have a wider width than the conductive non-ferromagnetic material 23. The base 21 may interlock with a slit 17 in the radial direction. For example, the slit 17 may have an inverted, inverted T-shaped, or dovetail shape in cross-section, and the metal strip 19' may have a corresponding T-shaped or dovetail cross-section. In this case, during manufacturing, the slit 17 may be opened from one end of the pole shoe body 13, allowing the metal strip 19' to be slid into the slit 17. This opening may then be closed, for example by means of bolting or otherwise attaching the metal strip 19' disposed in the slit 17 to one or both longitudinal axial ends of the end piece of the pole shoe body 13, thereby axially locking the position of the metal strip 19'.

[0076] In this example, the conductive non-ferromagnetic material 23 may be composed of, for example, copper or include copper (such as pure copper), copper alloys, austenitic stainless steel, nickel, or nickel alloys.

[0077] A conductive, non-ferromagnetic material 23 can be bonded to the base 21. This bonding can be, for example, a mechanical bonding using bolts, a chemical bonding, a thermal bonding such as welding, brazing, or soldering, a thermal solid bonding such as friction stir welding, or a bonding by compression.

[0078] Conductive grease can be applied between the metal strip 19' and the pole piece body 13. This increases the thermal and electrical conductivity between the metal strip 19' and the pole piece body 13.

[0079] In one example, each base 21 is made of the same material as the pole shoe body 13. Thus, for example, the base 21 and the pole shoe body 13 can be made of steel (such as the same type of steel).

[0080] In one example, conductive non-ferromagnetic material 23 can protrude radially from pole shoe body 13 and thus extend into the air gap between rotor 5 and stator 3.

[0081] In one example, the long side of the metal strip 19' may be coated with a soft and highly conductive material to form an interface with the pole piece body 13. This material could be, for example, silver. The material can be applied, for example, by electroplating.

[0082] Now refer to Figure 2 and Figure 6 Describe an example of manufacturing rotor 5.

[0083] In an example involving brazing, in the first step, M pole shoe bodies are provided, where M is the number of poles of the rotor 5. Next, a slit 17 is machined into the outermost radial surface of each pole shoe body 13, the slit being offset circumferentially from the plane of symmetry P in the intended hot spot region of the radial outer surface 15 of the pole shoe 11, as shown below. Figure 6 As shown. Then, a conductive non-ferromagnetic material is placed in the slit 17 and brazed to the pole shoe body 13. Subsequently, multiple openings 14 are drilled in the radially outer surface 15, including within the conductive non-ferromagnetic material. The pole shoe body 13 is then attached to the rotor core 7 by means of bolts in the multiple openings 14. The bolts in the openings 14 of the conductive non-ferromagnetic material can be radially countersunk below the conductive non-ferromagnetic material to retain only the pole shoe body 13. Therefore, the conductive non-ferromagnetic material can be held in place solely by brazing.

[0084] It has been found that brazing is a particularly suitable method for preparing pole shoes 11.

[0085] In some examples, the long side of the conductive non-ferromagnetic material may be provided with a coating compatible with the material of the pole piece body 13 for brazing.

[0086] The concept of the invention has been described above with reference to several examples. However, as will be readily understood by those skilled in the art, other embodiments besides those disclosed above are also possible within the scope of the concept of the invention as defined by the appended claims.

Claims

1. A rotor (5) for a synchronous motor (1), comprising: Rotor core (7), the rotor core having a longitudinal central axis (A), and Multiple salient poles (9), each salient pole including a pole shoe (11), the pole shoe being mounted to the rotor core (7) and forming the radial outermost portion of the corresponding salient pole (9), Each pole shoe (11) has a pole shoe body (13) provided with a longitudinal slit (17) extending primarily in a direction parallel to the longitudinal central axis (A). Each pole piece (11) includes a metal strip (19; 19') arranged in the slit (17), wherein each metal strip (19; 19') includes or is composed of a conductive non-ferromagnetic material (23), the conductive non-ferromagnetic material partially forming the radial outermost surface of the pole piece (11), and wherein the conductive non-ferromagnetic material (23) has a lower DC resistivity than the pole piece body (13).

2. The rotor (5) according to claim 1, wherein for each salient pole (9), the slit (17) is arranged to deviate from the plane of symmetry (P) in the circumferential direction of the rotor core (7), the plane of symmetry including the longitudinal central axis (A) and the longitudinal centerline of the corresponding salient pole (9).

3. The rotor (5) according to any one of the preceding claims, wherein the conductive non-ferromagnetic material (23) has a lower DC resistivity than iron.

4. The rotor (5) according to any one of the preceding claims, wherein the conductive non-ferromagnetic material (23) is copper or a copper alloy.

5. The rotor (5) according to any one of the preceding claims, wherein each pole shoe body (13) is made of a single piece of steel.

6. The rotor (5) according to any one of the preceding claims, wherein each metal strip (19') includes a base (21) on which the conductive non-ferromagnetic material (23) is disposed, the base (21) being disposed radially inside the conductive non-ferromagnetic material (23).

7. The rotor (5) according to claim 6, wherein the conductive non-ferromagnetic material (23) is bonded to the base (21).

8. The rotor (5) according to claim 6 or 7, wherein each base (21) is made of the same material as the pole shoe body (13).

9. The rotor (5) according to any one of claims 6 to 8, wherein each base (21) is interlocked with the corresponding pole shoe body (13) in the radial direction.

10. The rotor (5) according to any one of the preceding claims, wherein each pole shoe (11) has a central section located between a first axial end (11a) and a second axial end (11b) of the pole shoe (11), and wherein the conductive non-ferromagnetic material (23) in the slit (17) extends along the central section.

11. The rotor (5) according to any one of the preceding claims, wherein each pole shoe body (13) includes a single slit (17).

12. A synchronous motor (1), the synchronous motor comprising a rotor according to any one of the preceding claims.

13. An electric motor system (2), comprising: The synchronous motor (1) according to claim 12, and LCI (4), wherein the LCI is configured to drive the synchronous motor (1).

14. The motor system (2) according to claim 13, wherein the LCI (4) is an N-pulse LCI, wherein N is a positive integer multiple of 6, and wherein the radial thickness of the conductive non-ferromagnetic material (23) is at least half the skin depth of the maximum loss harmonic of the N-pulse LCI, which causes the maximum loss on the rotor (5) at a temperature of 150°C at the lowest frequency of occurrence of the LCI (4) and the synchronous motor (1) during normal operation.

15. The motor system (2) according to claim 14, wherein the conductive non-ferromagnetic material (23) provides a greater skin depth for the maximum loss harmonic than the pole shoe body (13).

Images