Demagnetizing device and demagnetizing method for magnetic steel of outer rotor of permanent magnet direct drive wind power motor

Abstract

The invention discloses a demagnetizing device and demagnetizing method for magnetic steel of an outer rotor of a permanent magnet direct-driven wind power motor, and belongs to the technical field of wind power generator assembly. The demagnetizing device comprises a fixed vertical plate, a vertical rib plate, a bottom plate, a hydraulic supporting column, a demagnetizing coil and a connecting cover plate; the fixed vertical plate, the vertical rib plate and the bottom plate are fixedly connected into a whole; the vertical rib plate is located on one side of the fixed vertical plate and is perpendicular to the fixed vertical plate, and the other side of the fixed vertical plate is connected with the demagnetizing coil through a hydraulic supporting column. The connecting cover plate and the bottom plate are located at the top and the bottom of the fixed vertical plate respectively, and threaded holes used for being fixedly connected with a rotor base are formed in the connecting cover plate and the bottom plate. According to the demagnetization tool, the demagnetization efficiency can be improved, and the demagnetization coil can demagnetize one or more magnetic poles at a time through the demagnetization method.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine assembly, and in particular to a demagnetization device and a demagnetization method for the outer rotor magnet of a permanent magnet direct-drive wind turbine. Background Art

[0002] Existing permanent magnet direct-drive wind turbines typically utilize an outer rotor and inner stator structure, with permanent magnets fixed to the inner wall of the outer rotor frame to form rows of magnetic poles. When this structure requires rotor repair or recycling, removing the magnets without demagnetizing them is difficult and cumbersome due to the strong magnetism of the permanent magnets. This requires specialized tooling and poses safety risks during handling.

[0003] Existing methods for demagnetizing the outer rotor magnets of permanent magnet wind turbine motors exploit their temperature sensitivity. Using an oxyacetylene flame or oven, the magnets are heated to above 310°C, causing them to lose their magnetism or even completely lose it, allowing them to be removed without losing their magnetism. However, permanent magnet direct-drive motors have a large number of outer rotor poles and are large in size. Heating all the magnets on the rotor takes a long time, consumes a lot of energy, and causes significant environmental pollution. Furthermore, high temperatures can damage the anti-oxidation layer on the permanent magnets, resulting in a loss of time and material costs.

[0004] In summary, the existing heating demagnetization method has many problems in the overall demagnetization process of the outer rotor structure of the permanent magnet direct-drive wind turbine motor, such as long heating time, high energy consumption, large environmental pollution, and large losses. There is an urgent need for a new demagnetization method for the outer rotor magnetic steel of the permanent magnet direct-drive wind turbine motor.

[0005] In the prior art, patent CN116130203B discloses a method for in-situ integral magnetization and demagnetization of a permanent magnet motor, comprising the following steps: alternately inserting prefabricated insulating layers and metal sheets along the air gap between the stator and rotor of the assembled permanent magnet motor, and then placing them into the gap between the magnetic poles to be magnetized or demagnetized on the stator or rotor, wherein the insulating layers and the metal sheets have the same size and structure, and the insulating layers and the metal sheets are alternately stacked to form a coil; connecting the coil to a power supply, and when the permanent magnet motor needs to be magnetized or supplemented with magnetism, passing current through both ends of the coil so that the direction of the magnetic field generated by the coil is the same as the magnetization direction of the magnetic pole to be magnetized; when the permanent magnet motor cannot be maintained by supplementing magnetism, the permanent magnet motor is demagnetized by passing an AC attenuation current through both ends of the coil.

[0006] However, this solution is only applicable to salient pole motors with inner rotors. The coil is wrapped around the magnetic poles, and a decaying oscillating current is passed through to perform demagnetization. It is not applicable to the outer rotors of permanent magnet direct-drive wind turbines, which use skewed pole surface-mounted magnets. In addition, the thickness of the magnetic poles will also limit the size of the coil, increasing the difficulty of manufacturing. Summary of the Invention

[0007] In order to solve the problem that there is currently no suitable method to demagnetize the outer rotor magnet of a permanent magnet direct-drive wind turbine, the present invention proposes a demagnetization device and a demagnetization method for the outer rotor magnet of a permanent magnet direct-drive wind turbine, which effectively solves the demagnetization problem of the outer rotor magnet of a permanent magnet direct-drive wind turbine, while improving the demagnetization efficiency and safety during the demagnetization process.

[0008] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows: A demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine motor comprises: a fixed vertical plate, a vertical rib plate, a bottom plate, a telescopic device, a demagnetization coil and a connecting cover plate; the fixed vertical plate, the vertical rib plate and the bottom plate are fixedly connected as a whole; the vertical rib plate is located on one side of the fixed vertical plate and is perpendicular to the fixed vertical plate, and the other side of the fixed vertical plate is connected to the demagnetization coil via the telescopic device; the connecting cover plate and the bottom plate are respectively located at the top and bottom of the fixed vertical plate, and both the connecting cover plate and the bottom plate are provided with threaded holes for connecting and fixing to the rotor base.

[0009] Furthermore, a plurality of transverse ribs are provided between the vertical ribs and the fixed vertical ribs.

[0010] Furthermore, the hydraulic support columns are provided in plurality and are evenly distributed on the fixed vertical plate.

[0011] Furthermore, a roller bracket I and a roller bracket II are respectively provided below the bottom plate on one side close to the vertical rib plate and on the other side close to the demagnetization coil, and rollers are connected to both roller brackets.

[0012] Furthermore, the roller bracket I and the roller bracket II are connected to the demagnetization tooling body by welding or bolting.

[0013] Furthermore, the connecting cover plate is provided with a stopper matched with the rotor base, and the matching surfaces of the connecting cover plate and the rotor base are transitionally matched.

[0014] Furthermore, the demagnetization coil covers a plurality of magnetic poles to be demagnetized, and demagnetization is performed by passing a damped oscillating current into the demagnetization coil.

[0015] Furthermore, the demagnetization coil covers a single magnetic pole to be demagnetized, and the demagnetization coil maintains the same inclination as the motor oblique pole. Demagnetization is performed by passing a unidirectional pulse current into the demagnetization coil to generate a unidirectional magnetic field opposite to the magnetization direction of the demagnetization pole.

[0016] Furthermore, the demagnetization coil uses a single coil to cover a single magnetic pole, or uses multiple adjacent and parallel coils to cover single magnetic poles respectively. When multiple adjacent and parallel coils are used, the connection methods of adjacent coils are opposite.

[0017] Based on the above-mentioned demagnetization device for the outer rotor magnet of a permanent magnet direct-drive wind turbine motor, the present invention also proposes a demagnetization method for the outer rotor magnet of a permanent magnet direct-drive wind turbine motor, comprising the following steps: Step 1: Connect and secure the demagnetization coil to the telescopic device on the demagnetization tool, then hoist it into the interior of the outer rotor. Lower the demagnetization tool until the bottom stop of its base is close to the mating surface of the machine base. Slowly move it closer to the rotor pole from the center of the circle until the bottom stop of the base is aligned with the mating surface of the machine base, and then lower the demagnetization tool. Step 2: Pre-install the screws and adjust the position of the demagnetization tool using the roller under the demagnetization tool base. When the screw holes on the demagnetization tool and the rotor base are aligned, securely fit the demagnetization tool and the rotor base. Step 3: Control the telescopic device on the demagnetization tooling to push the demagnetization coil toward the rotor pole so that it is completely in contact with the pole. Then, perform the demagnetization operation in three situations: The first demagnetization method is to cover multiple magnetic poles to be demagnetized with a demagnetization coil and pass a damped oscillating current through the demagnetization coil for demagnetization; The second demagnetization method: the demagnetization coil is a single coil covering a single magnetic pole, and a unidirectional pulse current is passed through the demagnetization coil to generate an instantaneous magnetic field in the opposite direction of the magnetization direction of the demagnetization pole for demagnetization; The third demagnetization method: the demagnetization coil uses multiple adjacent parallel coils to cover a single magnetic pole respectively. The wiring of adjacent coils is opposite. A unidirectional pulse current is passed through the demagnetization coil so that adjacent magnetic poles are subjected to the opposite demagnetization magnetic field to achieve demagnetization. Step 4. After the demagnetization of the magnetic pole is completed, remove the bolts fixing it to the rotor, control the telescopic device to retract the demagnetization coil, and move the coil position again by relying on the roller under the demagnetization tooling bottom plate until the demagnetization coil is aligned with the next demagnetization magnetic pole, and repeat the demagnetization operation from step 2 to step 3 until the demagnetization operation of the remaining magnetic poles is completed.

[0018] In summary, the present invention has the following advantages: 1. The present invention proposes a movable demagnetization tool that can be fixed to the rotor base. The demagnetization tool facilitates position replacement and fixation after demagnetization, thereby improving the demagnetization efficiency. 2. The demagnetization tooling of the present invention can form a rigid connection with the machine base. The ribs and the connecting cover on the demagnetization tooling together form a reinforcement structure of the demagnetization tooling, which can effectively resist the radial force of the rotor generated during the demagnetization process. 3. The demagnetization tooling of the present invention utilizes its own hydraulic support column and roller bracket to change and adjust the position of the demagnetization coil, making it easy to adjust the position of the demagnetization coil before demagnetization or transfer it to another magnetic pole for demagnetization after demagnetization, thus reducing the use of cranes and avoiding the problem of crane congestion. 4. The present invention can disperse the stress during the demagnetization process by cooperating with the base of the demagnetization tooling and the stopper of the connecting cover plate, thereby effectively ensuring the safety of the demagnetization process; 5. The present invention further extends the original stop design of the connecting cover on the demagnetization tool to form a larger contact surface, which transitions with the circumference of the machine base, disperses the stress on the machine base during the demagnetization process, and reduces the probability of deformation of the machine base.

[0019] 6. The present invention uses a magnetic field interference method to demagnetize, which shortens the demagnetization time, reduces environmental pollution, and reduces losses; 7. The present invention proposes a variety of demagnetization methods. One is to use a larger coil to cover multiple rotor poles, and pass an oscillating attenuation current to demagnetize multiple poles at the same time; the second is to place multiple coils adjacent to each other, each covering a single pole, and the wiring methods of adjacent coils are opposite. When a pulse current is passed, the current circulation directions are opposite, and the adjacent poles are subjected to reverse demagnetization magnetic fields, thereby realizing a multi-pole demagnetization of the reverse magnetic field demagnetization route; the third is to use a smaller coil to cover one rotor pole at a time, and pass a unidirectional pulse current to demagnetize the pole; the demagnetization coils of these three demagnetization methods can demagnetize one or more poles at a time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the overall structure of the demagnetization tooling of the present invention; Figure 2 A side view of the assembly of the demagnetization tooling and the rotor frame of the present invention; Figure 3 This is a schematic diagram of the installation of the improved connecting cover plate in Example 2 of the present invention; Figure 4 A top view of the assembly of the demagnetization tooling and the rotor base of the present invention; Figure 5 Schematic diagram of demagnetizing a single S magnetic pole in Example 4 of the present invention; Figure 6 Schematic diagram of demagnetizing a single N magnetic pole in Example 4 of the present invention; Figure 7 Schematic diagram of demagnetizing multiple magnetic poles in embodiment 4 of the present invention.

[0021] In the picture: 1. Fixed vertical plate; 2. Vertical rib plate; 3. Bottom plate; 4. Horizontal rib plate; 5. Hydraulic support column; 6. Demagnetization coil; 7. Connecting cover plate; 8. Roller bracket I; 9. Roller bracket II; 10. Rotor base; 11. Magnetic pole. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0024] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0025] In the description of the present invention, it should be noted that the terms "upper," "vertical," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is typically placed when in use, or are commonly understood by those skilled in the art. These terms are intended solely to facilitate the description of the present invention and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0027] Example 1 The present invention provides a demagnetization device for the outer rotor magnet of a permanent magnet direct drive wind turbine motor, such as Figure 1 、 Figure 2 and Figure 4 As shown, it includes a fixed vertical plate 1, a vertical rib plate 2, a bottom plate 3, a plurality of transverse rib plates 4, a hydraulic support column 5, a demagnetization coil 6 and a connecting cover plate 7.

[0028] The demagnetization fixture consists of a fixed vertical plate 1, vertical ribs 2, a bottom plate 3, and several transverse ribs 4 welded together. The vertical ribs 2 are located on one side of the fixed vertical plate 1 and perpendicular to it. A connecting cover 7 is located on top of the fixed vertical plate 1. Several transverse ribs 4 are connected between the vertical ribs 2 and the fixed vertical plate 1. The bottom plate 3 is located below the fixed vertical plate 1 and vertical ribs 2 and is provided with threaded connection holes.

[0029] Preferably, a plurality of threaded connection holes are provided on the connecting cover plate 7, and the connecting cover plate 7 and the fixed vertical plate 1 are engaged with each other through corresponding threaded holes.

[0030] The other side of the fixed vertical plate 1 is connected to the demagnetization coil 6 via a hydraulic support column 5. Preferably, four hydraulic support columns 5 are provided and evenly distributed on the fixed vertical plate 1.

[0031] Furthermore, a roller bracket I8 is provided below the base plate 3, near the side of the vertical rib plate 2, and a roller bracket II9 is ​​provided below the base plate 3, near the side of the demagnetization coil 6. Both roller brackets are connected to rollers. Preferably, roller bracket I8 and roller bracket II9 are connected to the demagnetization tooling body by welding or bolting.

[0032] During demagnetization, the connecting cover plate 7 and the bottom plate 3 are respectively fastened to the rotor base 10 by bolts to fix the demagnetization tooling.

[0033] Example 2 On the basis of Example 1, the demagnetization device for the outer rotor magnet of a permanent magnet direct-drive wind turbine motor of this embodiment further makes the following improvements: Since the rotor lacks radial support during the demagnetization process, the base cylinder is easily affected by stress and deformed. Therefore, in this embodiment, by changing the structure of the connecting cover plate 7 on the demagnetization tool, the original stop design is further extended to form a contact surface that prevents the base from deforming. A transition fit is adopted between the connecting cover plate 7 and the base mating surface, thereby dispersing the stress on the base during the demagnetization process and reducing the probability of base deformation. The improved structure of the connecting cover plate 7 is as follows: Figure 3 shown.

[0034] Example 3 Based on the content of the above-mentioned embodiment 1 or embodiment 2, the embodiment of the present invention further proposes a method for demagnetizing the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine motor, comprising the following steps: Step 1: Before demagnetization, fix the demagnetization coil 6 to the hydraulic support column 5 on the demagnetization tooling, lift it through the screw holes on the top connection cover 7 of the demagnetization tooling, and lift it to the inside of the outer rotor. Lower the demagnetization tooling until the bottom stop of its base plate 3 is close to the mating surface of the machine base. Slowly move it closer to the rotor magnetic pole from the center of the circle until the bottom stop of the base plate is aligned with the mating surface of the machine base, and then lower the demagnetization tooling; Step 2: Pre-install two screws and adjust the position of the demagnetization tooling by using the roller under the demagnetization tooling base 3. When the screw holes on the demagnetization tooling and the rotor base are aligned, firmly fit the demagnetization tooling and the rotor base. Figure 4 At this time, the connecting cover plate 7, the fixed vertical plate 1 and the rotor base 8 are fixed together; Step 3: Use the controller to synchronously operate the four hydraulic support columns 5 to push the demagnetization coil 6 toward the rotor poles, so that it fits completely with the poles and covers multiple poles; Step 4: Pass a damped oscillating current through the demagnetization coil 6 to perform demagnetization.

[0035] Step 5. After the demagnetization of the pole is completed, remove the bolts fixing it to the rotor and operate the hydraulic support column 5 to retract the demagnetization coil 6. There is no need to lift it again. Just use the roller bracket to push the demagnetization tooling along the circumference until the demagnetization coil 6 is aligned with the next demagnetization pole. Repeat the first demagnetization operation again to demagnetize the remaining poles.

[0036] During the above-described operation, the demagnetization fixture forms a rigid connection with the rotor frame. The ribs 2 and connecting cover 7 on the fixture together form a reinforced structure, effectively resisting the radial forces generated along the rotor during the demagnetization process. Simultaneously, the four hydraulic support columns 5 balance the support force on the back of the demagnetization coil 6. The stoppers on the demagnetization fixture's base plate 3 and connecting cover 7, mating with the rotor frame, disperse the stresses experienced during the demagnetization process, thereby ensuring safety.

[0037] Example 4 The advantages of demagnetizing by passing a damped oscillating magnetic field through the demagnetization coil in the third embodiment are high efficiency and the ability to demagnetize multiple adjacent magnetic poles simultaneously. However, the demagnetization coil 6 is subject to stress from multiple magnetic poles, requiring higher material strength and reinforcement for the demagnetization coil 6 . Furthermore, the energy required to generate the damped oscillating magnetic field is also higher.

[0038] Therefore, this embodiment proposes another demagnetization method for the outer rotor magnet of a permanent magnet direct-drive wind turbine, which uses a unidirectional pulse current to generate a unidirectional magnetic field in the demagnetization coil that is opposite to the magnetization direction of the demagnetization pole, thereby demagnetizing the pole.

[0039] This method not only has no demagnetization effect on adjacent magnetic poles with opposite polarity, but will cause the demagnetized magnet to become magnetized. Therefore, it can only demagnetize a single magnetic pole in isolation. However, the demagnetization coil is smaller than that in Example 3, the demagnetization coil is subjected to lower stress, and the requirements for the energy storage device are lower.

[0040] Regarding the technical route of this embodiment, its demagnetization tooling can be used interchangeably with that in Example 3, but the structure and arrangement of the demagnetization coil are different. Since the direct-drive wind turbine adopts a slanted pole design, the demagnetization coil in this embodiment should also be tilted and ensure that it only covers the current demagnetization pole. A unidirectional pulse current is passed through the demagnetization coil to generate an instantaneous magnetic field opposite to the magnetic pole magnetic field for demagnetization, such as Figure 5 and Figure 6 As shown. Figure 7 As shown, multiple coils can also be assembled adjacent to each other and side by side. The multiple side-by-side coils cover a single magnetic pole respectively. The wiring methods of adjacent coils are opposite. When a pulse current is passed through, the current circulation direction is opposite, and the adjacent magnetic poles are subjected to the opposite demagnetization magnetic field, thereby realizing a multi-pole demagnetization of the reverse magnetic field.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A demagnetization device for the outer rotor magnet of a permanent magnet direct-drive wind turbine, characterized in that: include: A fixed vertical plate (1), a vertical rib plate (2), a bottom plate (3), a telescopic device, a demagnetization coil (6) and a connecting cover plate (7); the fixed vertical plate (1), the vertical rib plate (2) and the bottom plate (3) are fixedly connected as a whole; the vertical rib plate (2) is located on one side of the fixed vertical plate (1) and is perpendicular to the fixed vertical plate (1), and the other side of the fixed vertical plate (1) is connected to the demagnetization coil (6) through the telescopic device; the connecting cover plate (7) and the bottom plate (3) are respectively located at the top and bottom of the fixed vertical plate (1), and both the connecting cover plate (7) and the bottom plate (3) are provided with threaded holes for connecting and fixing with the rotor base (10).

2. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 1, characterized in that: A plurality of transverse rib plates (4) are provided between the vertical rib plate (2) and the fixed vertical plate (1).

3. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 1, characterized in that: The telescopic devices are provided in plurality and are evenly distributed on the fixed vertical plate (1).

4. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 1, characterized in that: A roller bracket I (8) and a roller bracket II (9) are respectively provided below the bottom plate (3) on one side close to the rib plate (2) and on the other side close to the demagnetization coil (6), and rollers are connected to both roller brackets.

5. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 4, characterized in that: The roller bracket I (8) and the roller bracket II (9) are connected to the demagnetization tool body by welding or bolting.

6. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 1, characterized in that: The connecting cover plate (7) is provided with a stopper that matches the rotor base (10), and the matching surfaces of the connecting cover plate (7) and the rotor base (10) are transitionally matched.

7. A demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to any one of claims 1 to 6, characterized in that: The demagnetization coil (6) covers a plurality of magnetic poles (11) to be demagnetized, and demagnetization is performed by passing a decaying oscillating current into the demagnetization coil (6).

8. A demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to any one of claims 1 to 6, characterized in that: The demagnetization coil (6) covers a single magnetic pole (11) to be demagnetized, and the demagnetization coil (6) maintains the same inclination as the motor oblique pole, and demagnetization is performed by passing a unidirectional pulse current into the demagnetization coil (6) to generate a unidirectional magnetic field opposite to the magnetization direction of the demagnetization magnetic pole (11).

9. The demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine according to claim 8, characterized in that: The demagnetization coil (6) uses a single coil to cover a single magnetic pole (11), or uses multiple adjacent and parallel coils to cover the single magnetic poles (11) respectively. When multiple adjacent and parallel coils are used, the connection methods of adjacent coils are opposite.

10. A method for demagnetizing the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine motor, using the demagnetization device for the outer rotor magnetic steel of a permanent magnet direct-drive wind turbine motor according to any one of claims 1 to 9, characterized in that: The steps include: Step 1: Connect and fix the demagnetization coil (6) to the telescopic device on the demagnetization tool, then hoist it to the inside of the outer rotor, lower the demagnetization tool until the stop under the bottom plate (3) is close to the mating surface of the machine base, and slowly approach the rotor pole (11) from the center position until the stop under the bottom plate (3) is aligned with the mating surface of the machine base, and then lower the demagnetization tool; Step 2: Pre-install the screws and adjust the position of the demagnetization tooling by using the roller under the demagnetization tooling base (3). When the screw holes on the demagnetization tooling and the rotor base (10) are aligned, securely fit the demagnetization tooling and the rotor base (10); Step 3: Control the telescopic device on the demagnetization tool to push the demagnetization coil (6) toward the rotor magnetic pole (11) so that it is completely in contact with the magnetic pole (11), and then cover the demagnetization coil (6) with a plurality of magnetic poles (11) to be demagnetized, and pass an attenuated oscillating current into the demagnetization coil (6) for demagnetization; Step 4: After the demagnetization of the magnetic pole (11) is completed, remove the bolts fixing the rotor, control the telescopic device to retract the demagnetization coil (6), and move the coil position again by relying on the roller under the demagnetization tooling base (3) until the demagnetization coil (6) is aligned with the next demagnetization magnetic pole (11), and repeat the demagnetization operation of steps 2 to 3 until the demagnetization operation of the remaining magnetic poles (11) is completed.

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