Flat wire stator structure with in-slot constant width cooling channels and electric machine

Abstract

The application provides a flat wire stator structure with equal-width cooling flow channels in slots and a motor. The stator structure comprises a stator core and a stator winding. The stator core comprises a plurality of tooth portions, and a stator slot is formed between two adjacent tooth portions. The stator winding is composed of a conductor and is wound on the tooth portions. The conductor is wound on the tooth portions in multiple layers to form two conductor portions in the stator slot. A cooling flow channel for a cooling medium is formed between the two conductor portions. The width of the cooling flow channel remains unchanged in the direction from the slot bottom to the slot opening of the stator slot. The motor comprises the flat wire stator structure with equal-width cooling flow channels in slots. Compared with the prior art, the stator structure provided by the application has the following beneficial effects: the width of the cooling flow channel is controlled to remain unchanged, the trapezoidal flow channel in the traditional equal-width winding is replaced, the uniformity of the radial distribution of the cooling medium is improved, the temperature distribution of the winding is improved, and the local hot spot temperature is reduced.

Description

Technical Field

[0001] This invention relates to the field of motor technology, and specifically to a flat wire stator structure and motor with equal-width cooling channels in the slots. Background Technology

[0002] Against the backdrop of the accelerated development of global automotive electrification and aerospace electrification, drive motors are continuously evolving towards higher power density and higher efficiency. Conductor windings, due to their high bare copper slot fill factor and excellent thermal conductivity, have become one of the mainstream winding forms for propulsion systems in new energy vehicles and electric vertical takeoff and landing aircraft.

[0003] However, when the conductor motor operates at high speed and high frequency, the leakage magnetic field distribution within the stator slots exhibits significant spatial non-uniformity. Due to the combined effect of the alternating magnetic field of the armature current and the rotor permanent magnets, the leakage magnetic density in the slot opening region is much higher than that in the slot bottom region. Strong eddy current fields are induced within the conductors in this region, triggering skin effect and proximity effect, leading to a sharp increase in AC losses. Since the proportion of AC losses in total losses increases significantly with frequency, this phenomenon directly reduces the motor's operating efficiency at high speeds. Furthermore, in conductor motors using direct in-slot oil cooling, the cooling oil channels naturally formed between the left and right rows of conductors in a traditional equal-width conductor winding are trapezoidal, i.e., narrow at the slot bottom and wide at the slot opening. This trapezoidal oil channel has an excessively large flow cross-section and low flow velocity in the slot opening region, making it difficult to effectively remove heat from the loss concentration area, resulting in a greater temperature rise in the windings at the slot opening. These combined problems of concentrated losses and uneven cooling cause prominent local hot spots, further affecting the reliability of motor operation.

[0004] To address the high-frequency AC loss problem in conductor motors, existing suppression methods include using layered conductors in the slot opening region or replacing them with Litz wire to cut off eddy current paths. However, these methods often lead to a significant decrease in slot fill factor. Some researchers have also used high-resistivity materials to replace copper wire, which can suppress eddy current losses but simultaneously introduces the negative effect of increased DC losses. Furthermore, there are studies on optimizing leakage flux distribution by changing the winding topology or phase band arrangement, but their versatility is limited.

[0005] In summary, existing technologies either sacrifice slot fill factor to reduce AC losses, or prioritize increasing slot fill factor while encroaching on cooling space and failing to effectively suppress high-frequency eddy current losses, or introduce additional cooling components to enhance heat dissipation, thus encroaching on winding space. None of these methods effectively suppress high-frequency eddy current losses and simultaneously improve winding temperature rise without increasing copper usage or adjusting the basic electromagnetic design, solely through constraints on the conductor's shape. Therefore, there is an urgent need to provide a stator configuration suitable for external rotor motors that, under the constraints of equal single-turn cross-sectional area and constant total copper usage, synergistically reduces high-frequency AC losses and improves winding temperature rise. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned technical shortcomings and propose a flat wire stator structure and motor with equal-width cooling channels within the slots. This solves the problem that the cooling oil channels naturally formed between the left and right rows of conductors in existing conventional equal-width conductor windings are trapezoidal, with narrow bottoms and wide openings. The trapezoidal oil channels have excessively large cross-sections and low flow velocities in the slot opening region, making it difficult to effectively remove heat from the concentrated loss area, resulting in excessively high winding temperatures at the slot opening.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a flat wire stator structure with cooling channels of equal width within the slot, comprising: The stator core includes multiple teeth, with stator slots formed between two adjacent teeth; The stator winding is composed of conductors and wound on the teeth. The conductors are wound in multiple layers on the teeth to form two slot conductor portions in the stator slot. A cooling channel for cooling medium to pass through is formed between the two slot conductor portions, and the width of the cooling channel remains constant along the direction from the bottom of the stator slot to the slot opening.

[0008] In some embodiments, the stator core further includes a yoke, and a plurality of teeth are arranged circumferentially on the outer peripheral surface of the yoke, such that the direction from the bottom of the stator slot to the slot opening is the radial outward direction of the yoke.

[0009] In some embodiments, the outer peripheral surface of the yoke is a cylindrical structure, and the teeth are arranged at equal intervals around the yoke in the circumferential direction.

[0010] In some embodiments, the width of the teeth remains constant along the radial direction of the yoke.

[0011] In some embodiments, the width of the stator slot gradually increases along the direction from the bottom of the slot to the opening of the slot.

[0012] In some embodiments, along the direction from the bottom of the stator slot to the slot opening, the width of each layer of conductors in the conductor section of the slot gradually increases or increases in a stepped manner.

[0013] In some embodiments, along the direction from the bottom of the stator slot to the slot opening, the thickness of each layer of conductor in the conductor section of the slot gradually decreases or decreases in a stepwise manner.

[0014] In some embodiments, the cross-sectional area of ​​each layer of conductor in the inner trench is the same.

[0015] In some embodiments, the conductor surface is covered with an insulating layer, and the stator core is also covered with an insulating layer at the portion in contact with the conductor.

[0016] Secondly, the present invention also provides an electric motor, including the flat wire stator structure having equal-width cooling channels within the slots.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The flat wire stator structure with equal-width cooling channels in the slots provided by this invention forms a cooling channel for the cooling medium to pass through between the conductor portions in the two slots. The width of the cooling channel remains unchanged along the direction from the bottom of the stator slot to the slot opening, replacing the trapezoidal channel in the traditional equal-width winding. This improves the uniformity of the cooling medium distribution in the radial direction, improves the temperature distribution of the winding, and reduces the temperature of local hot spots. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the flat wire stator structure with equal-width cooling channels in the slot provided in an embodiment of the present invention within the stator slot; Figure 2 This is a schematic diagram comparing the conductor loss per turn of the winding in this embodiment with that of the control group under a certain high-frequency operating condition; Figure 3 This is a schematic diagram of the temperature distribution of a traditional winding with equal width and thickness. Figure 4 This is a schematic diagram of the temperature distribution of the winding in this embodiment.

[0019] Explanation of reference numerals in the attached drawings: 1. Tooth section; 2. Conductor section inside the groove; 21. Flat wire in the left column; 22. Flat wire in the right column; 3. Cooling channel. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] To address the technical problem of poor heat dissipation caused by excessively large flow cross-section and low flow velocity at the slot opening in existing stators with trapezoidal flow channels, this invention provides a flat wire stator structure with cooling flow channels of equal width within the slots, which can improve the temperature distribution of the windings and reduce the temperature of local hot spots.

[0022] Please see Figure 1 , Figure 1 This is a schematic diagram of the flat wire stator structure with equal-width cooling channels within the slots, provided in an embodiment of the present invention, within the stator slots. This flat wire stator structure with equal-width cooling channels within the slots includes a stator core and stator windings.

[0023] The stator core includes multiple teeth 1, and stator slots are formed between two adjacent teeth 1.

[0024] The stator winding is composed of conductors wound on tooth 1. Multiple layers of conductors are wound on tooth 1 to form two in-slot conductor portions 2 within the stator slots. Figure 1 The left column flat line 21 and the right column flat line 22 are shown in the diagram. A cooling channel 3 for the cooling medium to pass through is formed between the left column flat line 21 and the right column flat line 22. The width of the cooling channel remains constant along the direction from the bottom of the stator slot to the slot opening.

[0025] In some embodiments, the stator core further includes a yoke, and a plurality of teeth 1 are arranged circumferentially on the outer peripheral surface of the yoke, such that the direction from the bottom of the stator slot to the slot opening is the radial outward direction of the yoke.

[0026] Based on the above embodiments, the outer circumferential surface of the yoke is a cylindrical structure, and the teeth 1 are arranged at equal intervals around the yoke in the circumferential direction. That is, in these embodiments, the stator structure is the inner stator structure in an external rotor motor. The stator is located on the inner side, the rotor is located on the outer side, and the slot openings of the stator slots face the radially outward air gap.

[0027] Based on the above embodiments, the stator core adopts a parallel tooth structure, that is, the width of the tooth 1 remains unchanged along the radial direction of the yoke.

[0028] Based on the above embodiments, subject to this geometric constraint, the width of the stator slot gradually increases along the direction from the bottom of the stator slot to the slot opening.

[0029] Based on this, in order to keep the width of the cooling channel 3 constant, the width of each layer of conductors in the conductor section 2 inside the stator slot gradually increases or increases in a stepped manner along the direction from the bottom of the stator slot to the slot opening, in order to adapt to the gradually increasing width of the stator slot.

[0030] Based on the above embodiment, the thickness of each layer of conductor in the conductor section 2 inside the slot gradually decreases or decreases in a stepped manner along the direction from the bottom of the stator slot to the slot opening. This is to move the conductor section 2 inside the slot away from the slot opening region of the stator slot, thereby suppressing high-frequency AC losses.

[0031] Based on the above embodiment, the cross-sectional area of ​​each layer of conductor in the slot conductor section 2 is the same. This cross-sectional area is the same as the cross-sectional area of ​​a single turn conductor in a conventional equal-width, equal-thickness conductor winding within the stator slot, making the total copper consumption per slot in this embodiment consistent with the conventional approach. Therefore, this embodiment is on par with the conventional approach in terms of DC loss.

[0032] It is easy to understand that this stator structure has taken necessary insulation measures, including but not limited to covering the conductor surface with an insulation layer, and the stator core is also covered with an insulation layer in the part that contacts the conductor.

[0033] It should be noted that the overall design of this stator structure aims to simultaneously suppress high-frequency eddy current losses and enhance heat dissipation within the slots without increasing the overall copper usage of the windings or altering the basic electromagnetic design. This is achieved by increasing the conductor width and decreasing the thickness along the direction approaching the slot opening, leaving empty conductor layers in the slot opening region, and constructing a rectangular flow channel of equal width between the two conductor sections 2 within the slots. This reduces the conductor thickness at the slot opening and lowers the leakage magnetic flux density in that region, thereby reducing AC losses under high-frequency operating conditions. Furthermore, the equal-width rectangular flow channel improves the uniformity of the cooling medium distribution radially, enhances the heat transfer capacity in the slot opening region, and synergistically reduces the winding temperature rise.

[0034] Specifically, in this embodiment, both the left column flat wire 21 and the right column flat wire 22 are formed by radially stacking multiple turns of rectangular cross-section conductors. Within the same column, the cross-sectional area of ​​each turn of conductor is equal, and this cross-sectional area is the same as that of a single turn of conductor in the stator slot of a conventional equal-width and equal-thickness conductor winding, making the total copper consumption per slot of the winding in this embodiment consistent with the conventional scheme. Therefore, this embodiment is on par with the conventional scheme in terms of DC loss.

[0035] Because the stator slots employ a parallel tooth structure, the slot width gradually increases radially outwards. To maintain a constant width for the cooling channel 3, the conductor width in this embodiment increases radially outwards. Under the constraint of equal cross-sectional area for each turn, the increasing width necessarily corresponds to a decreasing thickness. The conductors closer to the bottom of the slot are narrower and thicker, while those closer to the slot opening are wider and thinner. This geometric gradient is determined by the spatial boundary of the slot and the constraint of equal cross-sectional area for each turn.

[0036] In the unequal width winding of this embodiment, since the width of each turn conductor increases radially outward layer by layer, the outer edges of the left and right columns of conductors are arranged in a stepped pattern. This embodiment constrains this: the average radial width of the inter-column gap between corresponding turns of conductors in the left and right columns remains constant, and this average width is not less than the minimum insulation spacing required by the motor design. This inter-column gap is a rectangular flow channel with uniform width from top to bottom, replacing the naturally formed trapezoidal flow channel in traditional equal width windings.

[0037] To verify the effectiveness of this embodiment in suppressing losses and temperature rise, a two-dimensional transient electromagnetic field simulation model was constructed. The control group used a conventional conductor winding of equal width and thickness, with the same cross-sectional area per turn and the same minimum width of the inter-row gap as in this embodiment. The same excitation current amplitude and frequency were applied to both models, and the average loss per turn of a single slot was compared.

[0038] Please see Figure 2 , Figure 2 This is a schematic diagram comparing the conductor loss per turn of the winding in this embodiment with that of the control group under a certain high-frequency operating condition.

[0039] The conductor numbers in the figure increase sequentially from the bottom of the slot to the slot opening. It can be seen that the overall loss of each turn of conductor in this embodiment is lower than that of the corresponding conductor in the control group, especially in the conductors near the slot opening where the loss reduction is more significant. For example, at conductor number 21 (near the slot opening), the loss of the conventional equal-width winding is 11.92W, while the loss of the winding in this embodiment is reduced to 8.08W, a reduction of 32.2%. This result indicates that, under the premise of constant total copper usage and satisfactory insulation gap, by varying the conductor width and thickness, combined with the vacant conductor layers in the slot opening, AC losses under high-frequency operating conditions can be effectively reduced, with a particularly prominent suppression effect on high-loss conductors in the slot opening.

[0040] Figure 3 and Figure 4 The diagrams show the temperature distribution of a conventional constant-width, constant-thickness winding and the winding of this embodiment, respectively. Under the same cooling flow rate, the highest temperature of the conventional constant-width, constant-thickness winding is 173.45℃, while the highest temperature of the constant cross-sectional area, unequal-width winding of this embodiment is 128.32℃, a temperature reduction of 45.13℃. This result indicates that the stator slots of this embodiment have rectangular flow channels, which can serve as cooling medium channels, allowing cooling oil or circulating air to dissipate heat. Reduced losses lead to fewer heat sources, and combined with the cooling effect of the flow channels, they improve the temperature distribution of the winding and reduce the temperature of local hot spots.

[0041] In other embodiments, the present invention also provides an electric motor including the aforementioned flat wire stator structure with equal-width cooling channels within the slots. Obviously, this motor also possesses the performance advantages of the aforementioned stator structure.

[0042] In summary, this stator structure and motor can achieve the following beneficial effects: For external rotor motors, under the constraints of equal cross-sectional area of ​​each turn and constant total copper usage, the conductor width increases along the direction closer to the slot opening, while the thickness decreases along the same direction. The reduced conductor thickness at the slot opening suppresses eddy currents within the conductor; simultaneously, the vacant conductor layers in the slot opening region reduce the leakage magnetic flux density experienced by the conductor in that region, thereby reducing AC losses under high-frequency operating conditions.

[0043] The average radial width of the inter-column gap between the left and right rows of conductors remains constant, forming a rectangular flow channel with uniform width at the top and bottom, replacing the naturally formed trapezoidal flow channel in traditional equal-width windings. This rectangular flow channel improves the uniformity of the radial distribution of the cooling medium, reduces heat sources due to reduced losses, improves the temperature distribution of the winding, and lowers the temperature of local hot spots.

[0044] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A flat wire stator structure with equal-width cooling channels within the slot, characterized in that, include: The stator core includes multiple teeth, with stator slots formed between two adjacent teeth; The stator winding is composed of conductors and wound on the teeth. The conductors are wound in multiple layers on the teeth to form two slot conductor portions in the stator slot. A cooling channel for cooling medium to pass through is formed between the two slot conductor portions, and the width of the cooling channel remains constant along the direction from the bottom of the stator slot to the slot opening.

2. The flat wire stator structure with equal-width cooling channels within the slot according to claim 1, characterized in that, The stator core also includes a yoke, and a plurality of teeth are arranged circumferentially on the outer circumferential surface of the yoke, such that the direction from the bottom of the stator slot to the slot opening is the radial outward direction of the yoke.

3. The flat wire stator structure with equal-width cooling channels within the slot according to claim 2, characterized in that, The outer circumferential surface of the yoke is a cylindrical structure, and the teeth are arranged at equal intervals around the circumference of the yoke.

4. The flat wire stator structure with equal-width cooling channels within the slot according to claim 3, characterized in that, The width of the teeth remains constant along the radial direction of the yoke.

5. The flat wire stator structure with equal-width cooling channels within the slot according to claim 1, characterized in that, The width of the stator slot gradually increases along the direction from the bottom of the slot to the opening of the slot.

6. The flat wire stator structure with equal-width cooling channels within the slot according to claim 5, characterized in that, Along the direction from the bottom of the stator slot to the slot opening, the width of each layer of conductors in the conductor section of the slot gradually increases or increases in a stepped manner.

7. The flat wire stator structure with equal-width cooling channels within the slot according to claim 6, characterized in that, Along the direction from the bottom of the stator slot to the slot opening, the thickness of each layer of conductor in the conductor section of the slot gradually decreases or decreases in a stepwise manner.

8. The flat wire stator structure with equal-width cooling channels within the slot according to claim 7, characterized in that, The cross-sectional area of ​​each layer of conductor in the conductor section of the groove is the same.

9. The flat wire stator structure with equal-width cooling channels within the slot according to claim 1, characterized in that, The conductor surface is covered with an insulating layer, and the stator core is also covered with an insulating layer in the part that contacts the conductor.

10. An electric motor, characterized in that, Includes the flat wire stator structure with equal-width cooling channels in the slot as described in any one of claims 1-9.

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