A coil manufacturing method for reducing ac loss of winding of a high-frequency motor

Abstract

The application discloses a coil preparation method for reducing winding AC loss of a high-frequency motor, and particularly relates to the field of energy-saving starting motors. In the application, the copper section required by a coil side is split into a plurality of independent insulated sub-conductors, and the sub-conductors are arranged into a two-layer matrix structure to form a sub-conductor flat wire bundle. The sub-conductor flat wire bundle is divided into a fixed section, a transposition window, an end backfolding section and a length compensation section along the length direction. The fixed section maintains the matrix structure, the transposition window performs adjacent position exchange and interlayer position exchange, the end backfolding section connects two in-slot straight sections, and the length compensation section applies controlled bending to the sub-conductors with a short path. Through position arrangement, local transposition, back-mirror image reset, path length compensation and sub-area solidification of the sub-conductors, the application reduces the AC copper loss caused by the skin effect, the proximity effect and the inter-sub-conductor circulation under the condition of maintaining the slot fill factor and the mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of energy-saving starter motor technology, and more specifically, to a method for preparing coils to reduce AC losses in the windings of a high-frequency motor. Background Technology

[0002] To reduce skin loss in a single thick conductor under high-frequency current, existing energy-saving starter motors typically split a single winding conductor into multiple thin conductors with independent insulation layers. These thin conductors are then arranged in parallel or continuously twisted to form a wire bundle. During manufacturing, the number and size of the thin conductors are selected according to the required copper cross-section of the winding. Multiple thin conductors are then output side-by-side using a wiring device, and the wire bundle shape is maintained through wrapping, bonding, or continuous twisting. After the wire bundle is prepared, it is wound into a coil with two straight sections in the slots and curved sections at the ends. The coil is then embedded in the stator slots, and the ends of each thin conductor are connected in parallel. When the motor is running, the current output from the driver is distributed to each thin conductor through the parallel connection points. All the thin conductors together form the coil current, and the rotating magnetic field generated by the coil drives the rotor to complete starting and operation.

[0003] When using a parallel arrangement structure, the radial and tangential positions of each thin conductor in the stator slot remain fixed. The thin conductors near the slot opening, bottom, and tooth sides experience different slot leakage magnetic fields, resulting in differences in the induced electromotive force and AC impedance of each conductor, and generating inter-strand circulating currents after parallel connection. While a continuous stranding structure can change the position of the thin conductors, continuous stranding increases the actual conductor length and the outer envelope of the wire harness, compressing the effective copper cross-section in the stator slot and increasing end dimensions, winding resistance, and embedding difficulty. Existing wire harness forming processes typically bend multiple thin conductors according to a uniform contour without DC resistance closed-loop compensation based on the actual path length of each conductor. This easily leads to path length differences between the inner and outer sides of the bend. Furthermore, when the wire harness is bonded as a whole before transposition or rigidly pressed directly in the transposition area, the thin conductors lack axial sliding space, easily causing varnish damage, localized warping, and resin buildup at intersections, affecting high-frequency loss control and long-term coil stability. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a coil preparation method for reducing AC losses in the windings of a high-frequency motor, and solves the problems mentioned in the background art through the following solution.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a coil to reduce AC losses in the windings of a high-frequency motor, comprising:

[0006] Step 1: Arrange multiple stranded conductors with independent insulation layers on their surfaces in a two-layer matrix structure to form a stranded flat wire bundle. Based on the stator slot size and effective core length of the high-frequency motor, determine two straight segments in the slot, end fold-back segments connecting the two straight segments in the slot, and fixed segments and three transposition windows located in each straight segment in the slot on the stranded flat wire bundle.

[0007] Step 2: Perform local pre-bonding on the fixed section to maintain the two-layer matrix structure of the multiple stranded conductors in the fixed section, and to keep the multiple stranded conductors in the transposition window in a state in which they can slide relative to each other along the length direction of the stranded flat wire bundle.

[0008] In the first straight segment within the slot, the first adjacent position exchange, interlayer position exchange, and second adjacent position exchange are performed sequentially through three transposition windows along the current entry direction. The first adjacent position exchange and the second adjacent position exchange are respectively used to exchange the tangential positions of adjacent stranded conductors in the same layer, and the interlayer position exchange is used to exchange the radial positions of two stranded conductors located in the same column.

[0009] In the second slot straight segment, along the current return direction, the second adjacent position exchange, interlayer position exchange, and first adjacent position exchange, which are mirror images of the spatial direction of the first slot straight segment, are carried out sequentially through the three transposition windows, so that each strand conductor returns to its initial matrix position after passing through the two slot straight segments.

[0010] Step 3: The split flat wire bundle with the position exchanged is loaded into the forming mold. The forming mold forms two straight segments in the groove and the end fold-back segment. A length compensation segment is set in the end fold-back segment. The four-wire DC resistance of each split conductor is measured, and the length compensation segment is adjusted according to the measurement results so that the absolute value of the deviation between the DC resistance of any one split conductor and the average DC resistance of all split conductors does not exceed 0.5% of the average DC resistance.

[0011] Step 4: Insulate and impregnate the formed stranded flat wire bundle with resin, constrain the shape of the fixed section, limit the transposition window with non-compression, and perform staged heating and curing to form an insulating and cured layer that covers the stranded flat wire bundle and penetrates between the adjacent stranded conductors.

[0012] Step 5: Connect the corresponding ends of each strand of conductor in parallel to obtain a coil assembly. Install the coil assembly into the stator slot and test the DC resistance and AC resistance of the coil assembly.

[0013] The technical effects and advantages of this invention are as follows:

[0014] 1. The present invention sets three spaced transposition windows in each slot straight segment, and through adjacent position exchange, interlayer position exchange, and re-adjacent position exchange, the tangential matrix position and radial matrix position of each strand conductor are changed respectively. The two slot straight segments adopt a transposition sequence that is a mirror image of each other in spatial direction, so that each strand conductor experiences complementary slot opening side position, slot bottom side position, and tooth side position in a complete coil, and returns to the initial matrix position after passing through two slot straight segments. This structure can balance the slot leakage magnetic field and induced electromotive force of each strand conductor, reduce the AC impedance difference and inter-strand circulating current caused by fixed position, and reduce the local current concentration caused by proximity effect.

[0015] 2. This solution only performs position exchange in three transposition windows and sets a fixed segment between adjacent transposition windows to maintain the two-layer matrix structure. It is not necessary to continuously twist the stranded conductors along the entire length of the coil. The fixed segment can maintain the cross-sectional size of the stranded flat wire bundle and the outer envelope of the winding. The transposition window is used to complete the position migration within a limited length range, thereby reducing the increase in conductor length, end size, and effective copper cross-section in the slot caused by continuous twisting. After the straight segments in the two slots are mirrored and transposed, each stranded conductor is restored to a uniform arrangement at the end of the coil. It is not necessary to add cross-connecting pieces at the end of the coil, which helps to reduce parallel connection points, shorten the end conductive path, and maintain the applicability of the existing winding equipment.

[0016] 3. Before forming the insulation curing layer, this solution uses a four-wire DC resistance measurement to measure each strand of conductor. A length compensation section is installed in the end fold-back section to adjust the shorter strands, ensuring that the absolute value of the deviation between the DC resistance of any single strand and the average DC resistance of all strands is controlled within 0.5%. This reduces uneven current distribution caused by path length differences. Local pre-bonding is implemented in the fixing section, and the transposition window maintains axial sliding capability during the forming stage. After forming, the insulation curing layer is formed through non-compression limiting and staged curing. This releases local stress generated by transposition and bending, reducing insulation damage at intersections, strand warping, and resin buildup. The combined effects of graded transposition, mirror reset, length compensation, and zoned curing enable the coil assembly to simultaneously achieve a stable matrix cross-section, balanced high-frequency current distribution, and reliable mechanical fixation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 This is a flowchart illustrating the transposition process of the flat strand wire bundle of the present invention.

[0019] Figure 3 This is a flowchart of the coil forming and insulation curing control process of the present invention.

[0020] Figure 4 This is a flowchart of the inspection and judgment process for the coil assembly of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] refer to Figures 1-4 The method for preparing a coil to reduce AC losses in the windings of a high-frequency motor, as shown, includes:

[0023] Step 1: Determine the harness parameters: Based on the stator slot size, effective core length, rated phase current, starting peak current, drive switching frequency and allowable temperature rise, determine the number of stranded conductors, cross-section of stranded conductors, matrix form of stranded flat harness, fixed section position, transposition window position, end foldback section outline and length compensation amount, and form a harness parameter sheet and position arrangement diagram.

[0024] First, obtain the slot opening width, slot body width, slot depth, slot insulation thickness, slot wedge dimensions, and allowable winding gap of the stator slot. Subtract the slot insulation, slot wedge, and assembly gap from the available slot cross-section to obtain the maximum outer envelope of the stranded flat wire harness. The width direction of the stranded flat wire harness is consistent with the tangential direction of the stator slot, and the thickness direction is consistent with the radial direction of the stator slot. Maintain a winding gap of 0.15 mm to 0.35 mm on one side between the stranded flat wire harness and the slot insulation, and a compression allowance of 0.20 mm to 0.50 mm between the stranded flat wire harness and the slot wedge.

[0025] Enameled copper flat wire is preferred for stranded conductors, but squared enameled round copper wire can also be used. For energy-saving starter motors with electrical frequencies between 500 Hz and 20 kHz, the thickness of the stranded conductors should be controlled between 0.20 mm and 0.60 mm, and the width between 0.60 mm and 1.80 mm. The insulation layer of the stranded conductors uses a composite varnish film with a heat resistance temperature of not less than 180 degrees Celsius, and the thickness of the varnish film on one side should be controlled between 0.025 mm and 0.060 mm. The fillet radius of the stranded conductors should be controlled between 0.08 mm and 0.25 mm to avoid damage to the insulation layer of adjacent stranded conductors by sharp corners during transposition.

[0026] The number of conductors is preferably eight, arranged in two layers and four columns. The layer closest to the slot opening is defined as the first layer, and the layer closest to the slot bottom is defined as the second layer. Along the stator circumference, from the left tooth side to the right tooth side, the columns are sequentially defined as the first, second, third, and fourth columns. The eight matrix positions are denoted as: First Layer, First Column; First Layer, Second Column; First Layer, Third Column; First Layer, Fourth Column; Second Layer, First Column; Second Layer, Second Column; Second Layer, Third Column; and Second Layer, Fourth Column. The eight conductors are numbered sequentially from first to eighth conductor, with the initial arrangement being: first to fourth conductors in the first layer, and fifth to eighth conductors in the second layer.

[0027] When the available slot width cannot accommodate a four-column structure, a two-layer, three-column structure with six stranded conductors can be used. When the single-slot current requires an increase in copper cross-section and the slot width is sufficient, a two-layer, five-column structure with ten stranded conductors can be used. Regardless of whether six, eight, or ten stranded conductors are used, the number of layers remains two. The transposition operation maintains three actions: adjacent position exchange, inter-layer position exchange, and re-adjacent position exchange. Changes in the number of matrix columns only affect the number of stranded conductors participating in each exchange.

[0028] Three transposition windows are determined based on the effective core length. Along the current-entry direction of the straight segment within the first slot, the starting point of the first straight segment is marked as the zero position, and the ending point as the full-length position. The center of the first transposition window is located at 20% to 28% of the effective core length, the center of the second transposition window is located at 47% to 53% of the effective core length, and the center of the third transposition window is located at 72% to 80% of the effective core length. The length of each transposition window is 6% to 10% of the effective core length, and the actual length of a single transposition window is not less than 18 mm. Fixed sections are maintained between adjacent transposition windows, and the straight sections at both ends of the straight segments within the slot are also considered fixed sections.

[0029] The first straight segment within the slot employs a forward hierarchical transposition. The first transposition window performs the first adjacent position exchange, specifically exchanging the first column of the first layer with the second column, the third column with the fourth column, the first column of the second layer with the second column, and the third column with the fourth column. The second transposition window performs inter-layer position exchange, specifically exchanging the first and second layer positions within the same column. The third transposition window performs the second adjacent position exchange, with the exchange direction consistent with the first transposition window. After the third transposition window is completed, the four stranded conductors originally located in the first layer enter the second layer, and the four stranded conductors originally located in the second layer enter the first layer. Simultaneously, each stranded conductor changes position at least once in the tangential direction.

[0030] The second slot's straight segment employs a reverse mirror transposition. Along the current return direction of the second slot's straight segment, the three transposition windows remain set at 20% to 28%, 47% to 53%, and 72% to 80%, but the transposition actions are sequentially: second adjacent position exchange, inter-layer position exchange, and first adjacent position exchange. Each transposition action in the second slot's straight segment has the opposite spatial direction to the corresponding action in the first slot's straight segment. After passing through two slot's straight segments, the stranded conductors restore their initial numbering order, ensuring that the coil's starting and ending ends maintain a uniform arrangement of the first to eighth stranded conductors.

[0031] The centerline length of the end fold-back section is determined based on the coil span and end height limit. The length compensation section is positioned within the outer arc region of the end fold-back section, within a width range close to the neutral plane, avoiding entry into the strong leakage magnetic field region near the stator slot. First, the theoretical path length of each strand of conductor is estimated based on the centerline of the forming die. Then, using the longest path as a benchmark, compensation amounts are allocated to the remaining strands. The compensation amount for a single strand of conductor is controlled between 0.3 mm and 3.0 mm. The length compensation section employs a planar S-shaped bend, with the radii of both reverse arcs not less than eight times the thickness of the strand of conductor. After length compensation, the difference in calculated path length between each strand of conductor is controlled within 0.4% of the longest path.

[0032] The wire harness parameter sheet must at least record the conductor material grade, bare copper dimensions, insulation layer thickness, number of conductors, matrix position, center position and length of the three transposition windows, fixed section length, end foldback outline dimensions, length compensation, forming radius, and inspection limits. The position arrangement diagram uses the same set of numbers throughout the material preparation, transposition, forming, curing, and inspection processes.

[0033] Step 2: Preparation of stranded flat wire bundle: Complete the laying, straightening, numbering, matrix arrangement, pre-bonding of fixed sections and transposition of transposition window according to the wire bundle parameter sheet to obtain a stranded flat wire bundle with a definite positional relationship and the ability to slide locally within the transposition window.

[0034] Eight stranded conductors are mounted on pay-off frames equipped with independent tension controllers. The pay-off tension of the first to eighth strands is controlled between 8 and 18 Newtons, with the tension difference between each pay-off channel not exceeding 2 Newtons at any given time. The stranded conductors pass sequentially through soft guide wheels, a horizontal straightening wheel set, and a vertical straightening wheel set. The working surfaces of the guide wheels are made of polyetheretherketone (PEEK) or polished ceramic, with a surface roughness not exceeding 0.4 micrometers. After straightening, the lateral bending of the stranded conductors within a 500 mm free length does not exceed 0.8 mm, and the torsion angle does not exceed 2 degrees.

[0035] A position marking station is set up at the straightening exit. Position markings are made by printing consecutive numbers on the outer surface of each stranded conductor using impregnable ink, or by using a laser to form light-colored marks on the insulation layer that do not penetrate it. The repeating interval of the position markings is controlled between 80 mm and 150 mm, and a directional marking is added before and after each transposition window. The directional marking consists of an arrow and the transposition window number, with the arrow pointing in the same direction as the fabrication direction of the stranded flat wire bundle.

[0036] Eight stranded conductors enter the matrix wiring mold. The matrix wiring mold has two layers of four rows of guide holes. The inlet radius of each guide hole is not less than 1 mm. The width of the guide hole is 0.05 mm to 0.12 mm wider than the stranded conductor width, and the height of the guide hole is 0.04 mm to 0.10 mm higher than the stranded conductor thickness. The matrix wiring mold outlet is equipped with upper and lower pressure plates and left and right limiting plates. The upper and lower pressure plates limit the thickness of the stranded flat wire bundle, and the left and right limiting plates limit the width of the stranded flat wire bundle. The unit length clamping force applied by the pressure plates is controlled between 20 N / m and 60 N / m, so that the stranded conductors fit together and can slide slightly axially.

[0037] The fixing section employs dot-matrix pre-bonding. The pre-bonding material is a thermosetting insulating film with a heat resistance temperature not lower than 180 degrees Celsius, and the film thickness is controlled between 0.03 mm and 0.08 mm. The film is applied only to the two wide surfaces of the stranded flat wire bundle, forming an adhesive strip with a width of 4 mm to 8 mm along the length of the fixing section, with a center-to-center spacing of 35 mm to 70 mm between adjacent adhesive strips. No adhesive film is applied within 10 mm of the transposition window and its two ends. The pre-bonding temperature is controlled between 110 degrees Celsius and 135 degrees Celsius, and the pressing time is controlled between 3 seconds and 8 seconds. After pressing, it is only necessary to ensure that the stranded conductors do not separate during handling to avoid overall hardening before transposition.

[0038] The first adjacent position exchange of the first transposition window is completed through a two-stage guide comb. The first-stage guide comb raises two adjacent strands of conductor in each layer to different heights, creating a vertical gap of 0.3 mm to 0.8 mm at the intersection. The second-stage guide comb interchanges the positions of two adjacent strands of conductor in the tangential direction. The axial projection length of the intersection segment is controlled between 55% and 75% of the transposition window length, and the lateral offset angle of a single strand of conductor within the intersection segment does not exceed 18 degrees. After transposition, the two-layer, four-column matrix is ​​restored using a shaping mold, with both the entrance and exit of the shaping mold using arc transitions.

[0039] The interlayer position exchange of the second transposition window is accomplished through four sets of staggered guide grooves. Each set of staggered guide grooves corresponds to two stranded conductors in the same column, allowing the first layer of stranded conductors to enter the second layer along a gentle slope, and the second layer of stranded conductors to enter the first layer along another gentle slope. The two gentle slopes are staggered by 6 mm to 15 mm in the axial direction to prevent the two stranded conductors from being rigidly squeezed at the same cross section. The minimum bending radius for interlayer position exchange is not less than ten times the thickness of the stranded conductors, and the change in interlayer height is completed continuously within the length of the transposition window.

[0040] The third transposition window uses the same guide comb as the first transposition window, but the installation position of the guide comb in the third transposition window is re-corresponding to the matrix arrangement after the second transposition window, ensuring that the conductors involved in the exchange are adjacent strands on the same layer after transposition. After completing the third transposition window, refer to the position arrangement diagram to read the position mark of each strand conductor and confirm that each strand conductor has entered the designated matrix position.

[0041] Pre-bonding is not performed when the stranded flat wire harness enters the end fold-back reserved area. The length of the end fold-back reserved area is increased by 20 mm to 40 mm according to the unfolded length of the forming mold, in order to absorb the slight slippage of each conductor during forming. The compensation marks of the length compensation section are pre-printed in the end fold-back reserved area, and the compensation marks include the compensation start point, compensation end point and compensation direction.

[0042] The three transposition windows corresponding to the straight segment within the second slot are completed on the same continuous stranded flat wire bundle. The transposition equipment changes the direction of the guide comb and the upper and lower staggered guide slots, sequentially performing the second adjacent position exchange, inter-layer position exchange, and first adjacent position exchange. After each transposition window is completed, the position marker is read through the top-view camera and the side-view camera. The top-view camera confirms the tangential column position, and the side-view camera confirms the radial layer position. If the identification result is inconsistent with the position arrangement diagram, the equipment stops traction and returns to the current transposition window to re-arrange the wires.

[0043] After all transpositions are completed, a visual and electrical pre-inspection is performed on the stranded flat wire harness. The visual inspection uses a 10x magnifying glass to examine the insulation layer inside the transposition window; the insulation layer should not show exposed copper, cracks, or continuous indentations. The electrical pre-inspection involves applying a 500V DC voltage between any two strands of conductor and holding it for 5 seconds; the insulation resistance should not be less than 100 megohms. The width tolerance of the stranded flat wire harness is controlled between ±0.10 mm and ±0.05 mm, and the thickness tolerance is controlled between ±0.08 mm and ±0.05 mm. After passing the pre-inspection, the wire harness is cut to the coil's unfolded length, leaving a parallel connection allowance of not less than 35 mm at the cut position.

[0044] Step 3: Complete coil forming: Insert the stranded flat wire bundle into the forming mold to form two straight segments in the slot, end fold-back segments and length compensation segments in sequence. Maintain the arrangement of the transposition windows during the forming process, and restore the uniform stranded conductor sequence at both ends of the coil through mirror verification.

[0045] The forming mold consists of two linear clamping seats, one end profile seat, three shifting window clearance slots, one length compensation pressure head, and an adjustable limiting block. The center distance between the two linear clamping seats is consistent with the coil span. The effective clamping length of the linear clamping seats covers the fixed section. The shifting window clearance slots correspond one-to-one with the three shifting windows. The depth of the shifting window clearance slots is 1 mm to 2 mm greater than the thickness of the split flat wire harness, and the width is 1 mm to 3 mm greater than the width of the split flat wire harness, so that the shifting windows do not bear direct clamping force during bending and pressing.

[0046] Place the stranded flat wire harness into the forming mold according to the position markings, with the straight section in the first slot on the inlet side and the straight section in the second slot on the return side. First close the first straight clamp, then close the second straight clamp. Lay a 0.3 mm to 0.8 mm thick silicone rubber protective pad on the clamping surface, and control the clamping pressure between 0.4 MPa and 1.2 MPa. After clamping, check the layer positions of the first to eighth stranded conductors using the position markings, confirming that both the inlet and return ends are aligned with the position arrangement. Figure 1 To.

[0047] The end fold-back section employs a staged bending process. The first stage involves bending the stranded flat wire bundle around the end profile seat to 60% to 75% of the designed angle, holding the pressure for 2 to 6 seconds, and then releasing 30% of the clamping pressure, causing a slight axial slippage of the stranded conductor within the reserved area of ​​the end fold-back section. The second stage completes the remaining bending angle and presses the end fold-back section into the end profile seat. The minimum bending radius inside the end fold-back section is no less than three times the total thickness of the stranded flat wire bundle and no less than twelve times the thickness of a single stranded conductor.

[0048] During the forming of the end fold section, the operator or equipment reads the compensation marks on each strand of conductor. Strands with shorter paths are pressed into a planar S-shape by a length compensation indenter, while strands with paths close to the reference length retain their natural curves. The length compensation indenter consists of two fixed cylindrical pins and one movable cylindrical pin, with the pin surface covered by a polyimide sleeve. The displacement of the movable cylindrical pin is set according to the wiring harness parameter sheet, ranging from 0.5 mm to 5 mm. After pressing, an insulation gap of at least 3 mm is maintained between the length compensation section and the main arc of the end fold section to prevent adjacent strands from contacting during vibration.

[0049] After the end fold-back section is formed, the transposition window undergoes conformal pressing. Conformal pressing uses an elastic pressing block to slowly roll along the length of the stranded flat wire bundle, with the rolling speed controlled between 10 and 30 millimeters per second, and the single pressing amount not exceeding 0.15 millimeters. The purpose of conformal pressing is to eliminate localized warping within the transposition window, restoring the designed outer envelope of the stranded flat wire bundle while preserving the insulation gaps between the stranded conductors. The transposition window is not rigidly flattened to prevent the enamel film at the crossing points from bearing concentrated loads.

[0050] Before removing the coil, take cross-sectional images of the end faces of the straight sections in both slots. The image recognition program determines the matrix position of each strand conductor according to the position markers and compares the actual position with the position arrangement diagram. If any strand conductor is in an incorrect layer or incorrect column position, the coil remains in the forming mold and is manually reset by opening the corresponding transposition window to allow the slot to vacate. A round-headed insulating lever is used for reset.

[0051] After completing the position verification, measure the parallelism, center distance, and torsion angle of the straight segments in the two slots. The deviation of the center distance between the straight segments in the two slots is controlled within ±0.20 mm, the straightness of a single straight segment in the slot within the effective core length is not greater than 0.30 mm, and the torsion angle of the cross section is not greater than 1.5 degrees. The deviation of the distance between the highest point of the end fold-back section and the reference surface of the forming mold is controlled within ±0.50 mm.

[0052] Perform a four-wire DC resistance measurement on each strand of conductor. Before measurement, remove 10 to 15 mm of insulation from the ends of the strands of conductors, and use a constant current source and Kelvin clamp for measurement. Use the average resistance of the eight strands of conductors as a reference, and the absolute value of the deviation of any single strand from the average value should not exceed 0.5%. When the deviation exceeds 0.5% but does not exceed 1.2%, adjust the length compensation section while keeping the coil uncured; when the deviation exceeds 1.2%, it is judged as an abnormal path arrangement or transposition forming, and it does not proceed to the next process.

[0053] After the DC resistance meets the requirements, the eight strands of the same coil are temporarily connected in parallel at the starting end and kept separated at the ending end. A pulse source is used to detect the inter-strand coupling response. The pulse rise time is controlled between 0.5 and 2 microseconds, and the pulse amplitude is controlled between 50 and 150 volts. If the response amplitude of any strand deviates from the median value of the eight strands by more than 8%, the corresponding transposition window is checked for layer errors, local flattening, or insulation damage. This detection is used to identify positional anomalies that are difficult to identify by DC resistance before insulation curing.

[0054] Step 4: Forming an insulating curing layer: The formed stranded flat wire bundle is subjected to zoned wrapping, preheating, vacuum impregnation, drip-drip adhesive removal, and staged curing to form an insulating curing layer that takes into account mechanical constraints, thermal conductivity, and inter-strand insulation, while retaining the smooth transition shape of the transposition window.

[0055] First, clean the coil surface. Use a lint-free cloth dampened with electronic-grade isopropyl alcohol to wipe away oil and dirt, then dry with hot air at a coil temperature of 40°C to 55°C for 15 to 30 minutes. Do not use chlorine-containing solvents during cleaning. Cover the parallel connection allowance at the ends of the stranded conductors with a heat-resistant protective sleeve to prevent the impregnating resin from covering the soldering area.

[0056] The straight sections within the groove are wrapped with polyimide film tape using a semi-overlapping method. The film tape thickness is controlled between 0.05 mm and 0.10 mm, and the wrapping tension is controlled between 8 N and 15 N. The overlap rate of the fixed section is controlled between 45% and 55%, and the overlap rate of the transposition window is controlled between 25% and 35%. The transposition window uses narrow film tape, with a width controlled between 6 mm and 10 mm, and it is applied circle by circle along the curve of the transposition window to prevent the wide film tape from forcibly flattening the intersection. At the end fold-back section, an additional layer of mesh insulating tape is added outside the length compensation section, with the mesh size controlled between 1 mm and 3 mm, to provide channels for the impregnating resin.

[0057] After coating, preheating is performed. The coil is placed in a hot air circulating oven and maintained at 80 to 100 degrees Celsius for 30 to 60 minutes to allow moisture to drain from the coil and reduce the viscosity resistance of the impregnating resin when it enters the gaps between the stranded conductors. After preheating, the coil is transferred to a vacuum impregnation tank within 10 minutes.

[0058] The impregnation resin uses a solvent-free, heat-resistant epoxy system or an unsaturated polyesterimide system, with a viscosity controlled between 150 mPa·s and 450 mPa·s at 25 degrees Celsius. After curing, the volume resistivity is not less than 1 x 10^14 ohm-cm. Spherical alumina particles with a diameter of 1 to 5 micrometers can be added to the resin, with the filler mass fraction controlled between 8% and 18% to improve the thermal conductivity of the cured insulating layer. After adding the filler, a vacuum planetary mixer is used to remove air bubbles; the resin is only introduced into the impregnation tank after the visible air bubbles have disappeared.

[0059] Vacuum impregnation consists of four stages: vacuuming, resin injection, pressure holding, and resin removal. In the vacuuming stage, the absolute pressure inside the tank is reduced to 3 kPa to 8 kPa and maintained for 20 to 40 minutes. In the resin injection stage, the vacuum is maintained, allowing the resin to slowly enter from the bottom of the tank and completely cover the coil. In the pressure holding stage, dry nitrogen is introduced into the tank, increasing the pressure to 0.25 MPa to 0.45 MPa and maintaining this pressure for 25 to 50 minutes. In the resin removal stage, the pressure is released, and the coil is suspended vertically in the straight section within the groove for 10 to 25 minutes, allowing excess resin to flow out through the transposition window and the end foldback section.

[0060] To prevent resin buildup in the insulation curing layer at the transposition window, low-pressure hot air is used to purge along the transposition window axis after adhesive removal. The hot air temperature is controlled between 45°C and 60°C, and the air pressure is controlled between 5 kPa and 15 kPa. Each transposition window is purged for 5 to 12 seconds. The purging only removes surface-accumulated resin and does not cause the film tape to shift. Subsequently, a flexible limiting clamp is installed on the outside of the transposition window. The inner cavity size of the flexible limiting clamp is 0.10 mm to 0.25 mm larger than the outer envelope of the multi-strand flat wire harness design. The flexible limiting clamp only restricts curing deformation and does not apply compressive force to the transposition window.

[0061] The curing process employs two temperature stages. The first stage is at 110°C to 130°C, held for 40 to 90 minutes, allowing the resin to enter a gel state and lock the stranded conductors in place. The second stage is at 155°C to 180°C, held for 90 to 180 minutes, allowing the insulation layer to complete cross-linking. The heating rate is controlled at 1 to 3°C per minute, and the oven door is opened only after cooling to 80°C. After curing, the flexible limiting clamps are removed, and the protective sleeves and residual resin on the surface of the parallel connections are cleaned.

[0062] After the insulation curing layer is completed, inspect the appearance and dimensions. The outer surface of the straight section within the groove should be continuous, without through cracks, resin voids, or sharp protrusions. The outer envelope of the transposition window must not exceed the dimensions specified in the wire harness parameter sheet by 0.20 mm. Use an industrial computed tomography (CT) scanner to randomly inspect the transposition windows, confirming that an insulation layer still exists between the stranded conductors and that there is no direct copper contact at the crossing points. If an industrial CT scanner is not available, a witness sample from the same batch can be made and inspected by cross-section. The witness sample should use the same stranded conductors, the same transposition window structure, and the same curing parameters.

[0063] Insulation electrical testing is performed before all stranded conductors are connected in parallel. A 1000V DC voltage is applied between any two stranded conductors and held for 10 seconds; the insulation resistance should be no less than 500 megohms. A 2000V power frequency voltage is applied between all stranded conductors and the external conductive foil and held for 60 seconds; no breakdown or flashover should occur. After the electrical testing is completed, the stranded conductors at the same end are connected in parallel according to the coil connection diagram. Parallel connections can be made using resistance welding, ultrasonic welding, or brazing, maintaining a thermal isolation distance of 8 mm to 15 mm between the welded area and the cured insulation layer. After welding, a tensile test is performed on each parallel connection point; the pull-out force of a single stranded conductor should be no less than 35% of the tensile bearing capacity of its bare copper cross-section.

[0064] Step 5: Assembly and Inspection: Install the coil assembly into the stator slot, complete the slot fixing, end connection and whole machine impregnation, and test the AC resistance, temperature rise and starting performance within the actual drive frequency range. Based on the test results, confirm whether the strand transposition structure meets the design requirements.

[0065] First, slot insulation is installed in the stator slots, with the length of the slot insulation extending beyond both ends of the core controlled between 3 mm and 8 mm. The two straight segments within the slots of the coil assembly are aligned with their corresponding stator slots, and an guide plate with a polyimide coating is used to guide the coil assembly into the stator slots. The winding thrust is applied evenly along the straight segments within the slots, with the peak thrust of a single straight segment not exceeding 800 N. When the transposition window is within the effective length of the core, the guide plate has a rounded clearance surface at the corresponding position of the transposition window to prevent the edges of the guide plate from pressing against the intersection.

[0066] After the coil assembly enters the stator slot, slot wedges are installed. Once the slot wedges are tightened, the stranded flat wire bundle must not show any visible looseness within the slot; the average compression of the stranded flat wire bundle by the slot wedges should be controlled between 0.05 mm and 0.20 mm. The end fold-back section is secured to the end support ring using fiberglass binding tape, with the binding points avoiding the length compensation section and the axial projection area of ​​the transposition window. Two to four binding points are provided at each coil end, with the binding tape width controlled between 4 mm and 8 mm.

[0067] After the phase-to-phase connection is completed, the entire machine is impregnated with a resin system compatible with the insulation curing layer. The impregnation is only used to fill gaps in the grooves and fix the ends; it does not alter the internal electrical connections of the stranded conductors. The curing temperature of the entire machine must not exceed the upper limit of the second temperature stage of the insulation curing layer, and the curing fixture must not be directly pressed onto the length compensation section.

[0068] AC resistance testing is performed before the stator is assembled with the rotor. A sinusoidal AC current is applied to a single phase winding, with test frequencies including at least 500 Hz, 2 kHz, 5 kHz, and the main switching frequency of the driver. The test current is 5% to 10% of the rated phase current to avoid significant temperature rise during the test. The DC resistance of the phase winding is measured simultaneously, and the ratio of AC resistance to DC resistance is used as the AC resistivity coefficient. A reference coil with identical copper cross-section, number of turns, span, slot fill factor, and end profile, but without a transposition window, is fabricated and measured using the same method. The design target for the AC resistivity coefficient of the low AC loss transposition coil of the high-frequency motor at 5 kHz and the main switching frequency of the driver is 72% to 88% of that of the reference coil, and the DC resistance must not exceed 103% of that of the reference coil.

[0069] If the AC resistivity does not meet the design target, first measure the consistency of the three-phase windings. If the three-phase deviation is within 3% and none of them meet the design target, check the conductor thickness, transposition window position, and slot leakage flux design. If the single-phase deviation exceeds 3%, check the position arrangement of the coil assembly for that phase, the parallel connection points, and the slot wedge compression. When measuring coil by coil using an impedance analyzer, if the AC resistivity of a certain coil deviates significantly from the other coils in the same phase, prioritize checking for transposition window layer errors or abnormal inter-strand insulation of that coil.

[0070] Temperature rise testing employs a repeated start-up condition. The power-on cycle is set based on the rated start-up time of the energy-saving starter motor. After each power-on, the machine is shut down for cooling according to the overall control strategy, and this process is repeated a specified number of times. Temperature sensors are arranged on the straight section inside the slot near the opening, the straight section inside the slot near the bottom, and the end bend section. The temperature rise difference at these three measuring points is used to determine whether the magnetic field exposure is balanced. With this scheme, the design objective is that the temperature rise difference between the measuring points at the opening and bottom of the slot does not exceed 8 degrees Celsius, and the temperature rise at the end bend section does not exceed the maximum temperature rise of the straight section inside the slot plus 5 degrees Celsius.

[0071] Record the starting performance test data, including peak starting current, time to reach target speed, single-start input energy, and highest winding temperature. Compared to the reference coil, the number of turns and copper cross-section of the coil assembly should remain consistent. The starting torque should not decrease, the single-start input energy should decrease, and the highest winding temperature after continuous starts should decrease. If the starting torque decreases while the DC resistance is normal, check for missing strands in the parallel connection at the ends. If the peak starting current increases while the AC resistivity is normal, check the controller parameters and air gap; do not attribute this phenomenon to the coil assembly.

[0072] The final inspection also includes appearance, dimensions, withstand voltage, inter-turn impact, and post-vibration retesting. The inter-turn impact voltage is selected based on the motor's rated voltage, and the waveform area difference is controlled within 5%. After the coil assembly completes the vibration test with the stator, the insulation resistance between the parallel ends of the stranded conductors and the stator core is measured again, and the 5 kHz AC resistivity is retested. The change in the retested value relative to the value before vibration does not exceed 3%, indicating that the transposition window and length compensation section remain stable under mechanical load.

[0073] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0074] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing a coil for reducing AC loss of a winding of a high frequency motor, characterized by, include: Step 1: Arrange multiple stranded conductors with independent insulation layers on their surfaces in a two-layer matrix structure to form a stranded flat wire bundle. Based on the stator slot size and effective core length of the high-frequency motor, determine two straight segments in the slot, end fold-back segments connecting the two straight segments in the slot, and fixed segments and three transposition windows located in each straight segment in the slot on the stranded flat wire bundle. Step 2: Perform local pre-bonding on the fixed section to maintain the two-layer matrix structure of the multiple stranded conductors in the fixed section, and to keep the multiple stranded conductors in the transposition window in a state in which they can slide relative to each other along the length direction of the stranded flat wire bundle. In the first straight segment within the slot, the first adjacent position exchange, interlayer position exchange, and second adjacent position exchange are performed sequentially through three transposition windows along the current entry direction. The first adjacent position exchange and the second adjacent position exchange are respectively used to exchange the tangential positions of adjacent stranded conductors in the same layer, and the interlayer position exchange is used to exchange the radial positions of two stranded conductors located in the same column. In the second slot straight segment, along the current return direction, the second adjacent position exchange, interlayer position exchange, and first adjacent position exchange, which are mirror images of the spatial direction of the first slot straight segment, are carried out sequentially through the three transposition windows, so that each strand conductor returns to its initial matrix position after passing through the two slot straight segments. Step 3: The split flat wire bundle with the position exchanged is loaded into the forming mold. The forming mold forms two straight segments in the groove and the end fold-back segment. A length compensation segment is set in the end fold-back segment. The four-wire DC resistance of each split conductor is measured, and the length compensation segment is adjusted according to the measurement results so that the absolute value of the deviation between the DC resistance of any one split conductor and the average DC resistance of all split conductors does not exceed 0.5% of the average DC resistance. Step 4: Insulate and impregnate the formed stranded flat wire bundle with resin, constrain the shape of the fixed section, limit the transposition window with non-compression, and perform staged heating and curing to form an insulating and cured layer that covers the stranded flat wire bundle and penetrates between the adjacent stranded conductors. Step 5: Connect the corresponding ends of each strand of conductor in parallel to obtain a coil assembly. Install the coil assembly into the stator slot and test the DC resistance and AC resistance of the coil assembly.

2. The method according to claim 1, characterized in that: The stranded flat wire bundle includes eight stranded conductors, which are arranged in a two-layer, four-column matrix structure. The layer closest to the stator slot opening is the first layer, the layer closest to the stator slot bottom is the second layer, and the first, second, third, and fourth columns are arranged sequentially along the tangential direction of the stator slot. The eight stranded conductors are, in order, the first stranded conductor, the second stranded conductor, the third stranded conductor, the fourth stranded conductor, the fifth stranded conductor, the sixth stranded conductor, the seventh stranded conductor, and the eighth stranded conductor. Before the position exchange, the first stranded conductor to the fourth stranded conductor are located in the first column to the fourth column of the first layer, and the fifth stranded conductor to the eighth stranded conductor are located in the first column to the fourth column of the second layer, respectively.

3. The method according to claim 1, characterized in that: With the starting point of each straight segment in the groove as the zero position and the ending point of each straight segment in the groove as the full length position, the centers of the three transposition windows are respectively located at 20% to 28%, 47% to 53%, and 72% to 80% of the length of the corresponding straight segment in the groove. The length of each of the transposition windows is 6% to 10% of the length of the straight section in the slot, and the length of each of the transposition windows is not less than 18 mm. A fixed section is provided between two adjacent transposition windows.

4. The method according to claim 1, characterized in that: The fixing section is partially pre-bonded by a thermosetting insulating film disposed on the two wide surfaces of the stranded flat wire harness, the thickness of which is 0.03 mm to 0.08 mm; The thermosetting insulating film forms an adhesive strip with a width of 4 mm to 8 mm along the length of the fixed section, and the center-to-center distance between adjacent adhesive strips is 35 mm to 70 mm. The thermosetting insulating film is not provided within a 10 mm range at each end of each of the transposition windows.

5. The method according to claim 1, characterized in that: When the first adjacent position is swapped and the second adjacent position is swapped, the two stranded conductors that need to be swapped in the tangential direction are first made to have a radial gap of 0.3 mm to 0.8 mm, and then the two stranded conductors are moved in opposite tangential directions and the matrix column positions are swapped. The axial projection length of the intersection segment of the two stranded conductors in the corresponding transposition window is 55% to 75% of the length of the transposition window, and the tangential offset angle of a single stranded conductor in the intersection segment does not exceed 18 degrees. During the interlayer position exchange, the two stranded conductors in the same column exchange matrix layer positions along two axially offset bending paths. The offset distance between the two bending paths along the length direction of the stranded flat wire bundle is 6 mm to 15 mm, and the minimum bending radius in the interlayer position exchange is not less than ten times the thickness of the stranded conductor.

6. The method according to claim 1, characterized in that: The end fold-back section is formed by two-stage bending. In the first stage, the stranded flat wire bundle is bent to 60% to 75% of the designed bending angle. After reducing the clamping pressure of the forming mold, the multiple stranded conductors are axially relative to each other along the end fold-back section. In the second stage, the remaining bending of the end fold-back section is completed. The length compensation section is located in the outer arc region of the end fold section and forms a planar S-shaped bend on the stranded conductor where the path length is less than the reference path length. The path compensation amount of a single stranded conductor is 0.3 mm to 3.0 mm. The planar S-shaped bend includes two arcs in opposite directions, and the radius of each arc is not less than eight times the thickness of the stranded conductor.

7. The method according to claim 1, characterized in that: Before the insulation curing layer is formed, a four-wire DC resistance measurement is performed on each of the stranded conductors. When the absolute value of the deviation between the DC resistance of any one of the stranded conductors and the average value of the DC resistance is greater than 0.5% of the average value of the DC resistance and not greater than 1.2% of the average value of the DC resistance, the path length of the corresponding stranded conductor is changed by adjusting the length compensation segment of the corresponding stranded conductor. When the absolute value of the deviation is greater than 1.2% of the average value of the DC resistance, check the matrix position and crossover pattern of the corresponding strand conductor in the transposition window.

8. The method according to claim 1, characterized in that: The resin impregnation process includes preheating, vacuuming, vacuum glue feeding, pressure impregnation, and glue discharge in sequence. During the vacuuming process, the absolute pressure is controlled at 3 kPa to 8 kPa and maintained for 20 to 40 minutes; during the pressure impregnation process, the pressure is controlled at 0.25 MPa to 0.45 MPa and maintained for 25 to 50 minutes. The phased heating and curing includes a first temperature stage and a second temperature stage. The temperature of the first temperature stage is 110 degrees Celsius to 130 degrees Celsius, and the holding time is 40 minutes to 90 minutes. The temperature of the second temperature stage is 155 degrees Celsius to 180 degrees Celsius, and the holding time is 90 minutes to 180 minutes. The non-compression limiting mechanism employs a flexible limiting clip disposed outside the switching window, wherein the inner cavity size of the flexible limiting clip is increased by 0.10 mm to 0.25 mm relative to the designed outer envelope size of the switching window.

9. The method according to claim 1, characterized in that: Multiple stranded conductors are arranged in a two-layer matrix structure to form a stranded flat wire bundle. The stranded flat wire bundle includes two straight segments in the slot and an end fold-back segment connecting the two straight segments in the slot. Each straight segment in the slot includes a fixed segment and three transposition windows spaced apart along the length of the straight segment in the slot. The three transposition windows in the first straight segment of the slot sequentially include an adjacent position exchange structure, an inter-layer position exchange structure, and an adjacent position exchange structure; the three transposition windows in the second straight segment of the slot sequentially include an adjacent position exchange structure, an inter-layer position exchange structure, and an adjacent position exchange structure that are mirror images of the spatial direction of the first straight segment of the slot. Each of the stranded conductors changes its radial matrix position and tangential matrix position in the two straight segments within the slots, and returns to its initial matrix position after passing through the two straight segments within the slots. The end fold-back section is provided with a length compensation section to make the DC resistance of each strand of conductor tend to be consistent, and the absolute value of the deviation between the DC resistance of any single strand of conductor and the average DC resistance of all strands of conductor does not exceed 0.5% of the average DC resistance. An insulating curing layer is provided on the outside of the stranded flat wire bundle. The insulating curing layer penetrates between adjacent stranded conductors and fixes the shape of the fixing section and the transposition window.

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