Air-gap adjustable double-stator single-rotor permanent-magnet disc motor and control method thereof

Abstract

This invention discloses an air-gap adjustable dual-stator single-rotor permanent magnet disc motor and its control method. The technical solution includes a housing, a stator, and end covers. End covers are installed at both ends of the housing. The stator is mounted on one side of a stator back plate, and the stator back plate and end covers are connected by multiple positioning guide rods. Multiple guide rod hydraulic cylinders are distributed circumferentially inside the housing. The ends of the guide rod hydraulic cylinders contact the stator back plate, and the hydraulic cylinders can move the stator axially to adjust the air gap length. This invention changes the air gap length by moving the stator axially, requiring the stator windings to provide a direct-axis current component, which improves motor efficiency, saves excitation current, and reduces the risk of permanent magnet demagnetization.

Description

Technical Field

[0001] This invention relates to the field of electric motors, and more particularly to a dual-stator single-rotor permanent magnet motor with adjustable air gap and its control method. Background Technology

[0002] Currently, steam turbine generators use current-excited synchronous generators. These generators can adjust the air gap magnetic field by changing the excitation current, thereby regulating the output voltage and stabilizing it easily. Although permanent magnet motors are highly efficient, their air gap magnetic field is provided by permanent magnets. Therefore, adjusting the air gap magnetic field is typically achieved by adjusting the direct-axis current component of the stator winding current, commonly known as field weakening speed control, to achieve high-speed operation. This method of adjusting the air gap magnetic field is widely used in engineering for permanent magnet motors. However, for permanent magnet generators, this method is more difficult to implement in engineering, which is why current steam turbine generators all use current-excited synchronous generators. This field weakening speed control method requires additional field weakening current from the stator winding, increasing stator winding copper losses and requiring additional field weakening energy from the power supply. For traditional cylindrical radial flux permanent magnet motors, since the air gap length cannot be adjusted, the air gap magnetic field can only be adjusted by adjusting the direct-axis current component of the stator winding current.

[0003] Unlike radial flux motors, disc motors have their stator and rotor arranged axially, and the length of their air gap can be adjusted axially. This means that the size of the air gap magnetic field can be adjusted by changing the length of the air gap, thereby achieving field weakening speed regulation (permanent magnetic disc motor) or stable output voltage (permanent magnetic disc generator).

[0004] Regarding patent applications for disc motors with adjustable air gaps, existing technologies propose a disc motor with adjustable air gaps. This involves using a turbine motor to drive the axial movement of the bearing cover, thereby achieving axial movement of the rotor disc and adjusting the air gap size. While this method is feasible, it is only applicable to single-disc disc motors. For dual-rotor single-stator or dual-stator single-rotor disc motors, the presence of dual air gaps prevents air gap adjustment. The proposed disc motor air gap adjustment control method employs three fixed-point values: minimum air gap, maximum air gap, and constant air gap, which cannot achieve the stepless speed regulation of current electric vehicle motors or the continuous pressure regulation of steam turbines.

[0005] Existing technology also discloses a disc motor with adjustable stator-rotor air gap. For a dual-stator, single-rotor disc motor, it uses the rotation of screws to control the axial displacement of the stators on both sides of the rotor disc, thereby adjusting the air gap size. While this invention can adjust the air gap size, it cannot fix the relative axial position of the rotor disc and the two stator discs, meaning it cannot guarantee that the air gap sizes on both sides of the rotor disc are equal. This method of adjusting the air gap easily leads to unequal air gap sizes on both sides of the rotor disc. Furthermore, this method requires multiple screws arranged circumferentially along the stator disc, and these screws need to be highly consistent. In addition, this method of adjusting the air gap is difficult to automate.

[0006] Existing technology discloses an adjustable-gap disc motor and a range-extended electric vehicle, which adjusts the air gap size of the disc motor using the gas pressure of an external air source. Since the rotor disc rotates, a certain gap must remain between its outer circumference and the housing. Therefore, this method cannot adjust the air gap size of the disc motor by adjusting the air pressure within the air gap. Existing technology also proposes an adjustable-gap permanent magnet coreless disc motor, in which a worm gear drives a thrust bearing sleeve to rotate, and this, in conjunction with an intermediate end cover, achieves axial movement of the rotor disc. This invention has the following problems: First, this method can only adjust the air gap on one side; since the stator cannot move with it, the other air gap cannot be adjusted. Second, an additional intermediate end cover needs to be added inside the motor, which is very difficult to manufacture. Summary of the Invention

[0007] To overcome the above-mentioned technical problems, the present invention provides a dual-stator single-rotor permanent magnet motor with adjustable air gap and its control method. By moving the stator along the axial direction to change the air gap length, the stator winding needs to provide a direct-axis current component, which improves motor efficiency, saves excitation current, and reduces the risk of permanent magnet demagnetization.

[0008] The technical solution adopted by this invention to solve its technical problem is as follows:

[0009] An air gap adjustable dual-stator single-rotor permanent magnet motor includes a housing, a stator and end covers. End covers are installed at both ends of the housing. The stator is installed on one side of the stator back plate. The stator back plate and the end covers are connected by multiple positioning guide rods.

[0010] Multiple guide rod hydraulic cylinders are distributed circumferentially inside the housing. The ends of the guide rod hydraulic cylinders contact the stator back plate. The hydraulic cylinders can move the stator axially to adjust the air gap length.

[0011] Furthermore, the positioning guide rod is fitted with a spring, which is located between the stator back plate and the end cover.

[0012] Furthermore, the stator back plate has multiple first positioning holes circumferentially provided for installing positioning guide rods, and the end cover has multiple second positioning holes correspondingly provided.

[0013] Furthermore, the positioning guide rod has a threaded section, and the second positioning hole is a threaded hole that is adapted to the threaded section of the positioning guide rod;

[0014] The end of the positioning guide rod furthest from the threaded section has a polygonal head structure.

[0015] Furthermore, the guide rod hydraulic cylinder is fixed to the housing, and the inlet and outlet of the guide rod hydraulic cylinder are connected to conduits, which extend out of the housing.

[0016] Furthermore, the conduits located on the same end cap side of the housing are connected in parallel and connected to a hydraulic pump.

[0017] Furthermore, the conduit is fitted with a valve.

[0018] Furthermore, a rotor disk is provided between the two stators, and the rotor disk is mounted on the rotating shaft; voltage test coils are pre-embedded in the stator windings.

[0019] A control method for a dual-stator single-rotor permanent magnet disc motor with adjustable air gap includes:

[0020] When it is necessary to increase the air gap of the motor, the hydraulic pump increases the oil pressure in the hydraulic cylinder of the guide rod, which pushes the guide rod to move, causing the stator back plate and stator to move toward the end cover side, thus increasing the air gap of the motor; when the air gap increases to meet the requirements, the valve closes.

[0021] When it is necessary to reduce the air gap of the motor, open the inlet and outlet valves of the guide rod hydraulic cylinder to return the hydraulic oil to the hydraulic pump, reduce the oil pressure of the hydraulic pump, and under the action of the spring and axial magnetic pull, the stator back plate and stator move towards the rotor disk to reduce the air gap of the motor until the test coil voltage meets the requirements.

[0022] Furthermore, if the voltages on both ends of the cover are not equal, after closing the valve on one side, adjust the oil pressure of the hydraulic cylinder on the other side of the guide rod until the voltages on both sides are equal.

[0023] The beneficial effects of this invention are:

[0024] (1) The present invention adjusts the air gap size of the permanent magnet motor by pushing the stator axially to move through the guide rod hydraulic cylinder. Compared with the commonly used method of adjusting the air gap magnetic field by using the direct axis current component of the stator winding, the present invention directly changes the air gap length by using a mechanical structure, without the need for the stator winding to provide the direct axis current component, thereby improving motor efficiency and saving excitation current.

[0025] (2) The present invention uses the method of changing the air gap length when adjusting the air gap magnetic field. Compared with the method of adjusting the air gap magnetic field by using the direct axis current component of the stator winding, the risk of permanent magnet demagnetization is greatly reduced.

[0026] (3) Compared with the method of adjusting the air gap magnetic field by using the direct axis current component of the stator winding, the present invention has a larger air gap magnetic field adjustment range, that is, it has a larger speed regulation or voltage regulation range for motors or generators.

[0027] (4) The present invention uses a miniature guide rod hydraulic cylinder to drive the stator to move axially to achieve the air gap size. The control method is to measure the voltage of the motor test coil in real time and adjust the hydraulic cylinder pressure until the speed regulation or pressure stabilization requirements are met. The control method is simple and easy to implement. Attached Figure Description

[0028] Figure 1 This is an overall structural diagram of the present invention;

[0029] Figure 2 This is a schematic diagram of the stator fixing according to the present invention;

[0030] Figure 3 This is a schematic diagram of the stator guide rod of the present invention;

[0031] Figure 4 This is a schematic diagram of the stator equipped with a miniature hydraulic cylinder according to the present invention;

[0032] Figure 5 This is a schematic diagram showing the connection between the miniature guide rod hydraulic cylinder and the stator back plate of the present invention;

[0033] Figure 6 This is a schematic diagram of the internal structure of the disc motor of the present invention;

[0034] Figure 7 This is a flowchart of the field weakening speed control of the permanent magnet motor of the present invention;

[0035] Figure 8 This is a flowchart illustrating the output voltage adjustment control of the permanent magnet disc generator of the present invention.

[0036] Among them, 1. Stator, 11. Iron core, 12. Stator back plate, 13. First positioning hole, 14. Winding, 2. End cover, 21. Front end cover, 22. Rear end cover, 23. Second positioning hole, 3. Positioning guide rod, 31. Threaded section, 32. Head, 33. Spring, 4. Guide rod hydraulic cylinder, 41. Guide rod, 42. Inlet and outlet, 43. Fixing hole, 44. Bolt, 45. Conduit, 5. Housing, 6. Rotating shaft, 7. Rotor disc. Detailed Implementation

[0037] Example 1:

[0038] Refer to the instruction manual appendix Figure 1 -Appendix Figure 6 The following is a detailed description of a dual-stator single-rotor permanent magnet motor with adjustable air gap according to the present invention.

[0039] This embodiment provides a dual-stator single-rotor permanent magnet motor with adjustable air gap, such as... Figure 1 and Figure 6 As shown, it includes a housing 5, a stator 1, an end cover 2, a rotating shaft 6 and a rotor disk 7. The rotating shaft 6 is installed in the center of the housing 5, and two stators 1 are installed on the rotating shaft 6. The rotor disk 7 is installed between the two stators 1 to form a double-stator single-rotor structure. End covers 2 are installed at both ends of the housing 5, namely the front end cover 21 and the rear end cover 22.

[0040] Furthermore, such as Figure 2 and Figure 4 As shown, the stator 1 is fixed on one side of the stator back plate 12. The stator 1 includes an iron core 11 and a winding 14. Several turns of voltage test coil are pre-embedded in the winding 14. The voltage across the voltage test coil is proportional to the motor's no-load back electromotive force (the proportionality is related to the number of turns of the test coil and the number of turns in series per phase). By measuring the voltage of the test coil, the magnitude of the motor's back electromotive force can be calculated based on the proportional relationship.

[0041] The stator 1 is connected to the end cover 2 by multiple circumferentially spaced positioning guide rods 3, which axially position the end cover 2. The number of positioning guide rods 3 is selected according to actual requirements; in this embodiment, six positioning guide rods 3 are provided.

[0042] like Figure 3 As shown, the positioning guide rod 3 has a head 32 at one end, which is a polygonal structure. In this embodiment, the head 32 is set in an external hexagonal shape, which serves as both a bolt tightening / loosening mechanism and a clamping mechanism for the stator back plate 12. Therefore, the hexagonal head 32 needs to be machined into a flat surface.

[0043] The positioning guide rod 3 has a cylindrical structure and a threaded section 31, which forms a threaded connection with the end cap 2. To securely fix the positioning guide rod 3 to the end cap 2, thread-locking adhesive needs to be applied to the threaded section 31 during fixing.

[0044] Although there is a large axial magnetic pull between the stator 1 and the rotor, a spring 33 of a certain length is provided between the end cover 2 and the stator back plate 12 to ensure that the force is balanced. The spring 33 is sleeved on the rod body of the positioning guide rod 3, between the threaded section 31 and the head 32; after the positioning guide rod 3 is connected to the end cover 2 and the stator back plate 12, there is a pre-compression force between the spring 33 and the stator back plate 12.

[0045] Furthermore, the stator back plate 12 has the same number of first positioning holes 13 as the positioning guide rods 3 in the circumferential direction, and the end cover 2 has the same number of second positioning holes 23 at the corresponding positions. The second positioning holes 23 are threaded holes to cooperate with the threaded section 31 of the positioning guide rods 3 to form a threaded connection.

[0046] The size of the air gap of the motor is achieved by adjusting the position of the stator back plate 12. In this embodiment, multiple guide rod hydraulic cylinders 4 (e.g., 3) are arranged along the inner circumference of the housing 5. The stator back plate 12 and the stator 1 are moved axially by extending and retracting the guide rod hydraulic cylinders 4, thereby changing the distance between the two stator back plates 12 and adjusting the length of the air gap.

[0047] In this embodiment, the guide rod hydraulic cylinder 4 is a miniature guide rod hydraulic cylinder; such as Figure 5 As shown, the guide rod 41 of the guide rod hydraulic cylinder 4 contacts the stator back plate 12, and the axial direction of the guide rod 41 is parallel to the axis of the rotating shaft 6. The guide rod hydraulic cylinder 4 has several fixing holes 43, and bolts 44 are installed in the fixing holes 43 to fix it to the housing 5.

[0048] The guide rod hydraulic cylinder 4 is provided with inlet and outlet 42, and the inlet and outlet 42 are connected to conduit 45, which extends from the surface of housing 5; the conduits 45 located on the front end cover 21 side are connected in parallel to each other and connected to the hydraulic pump; the conduits 45 located on the rear end cover 22 side are connected in parallel to each other and connected to the hydraulic pump; each conduit 45 is equipped with a valve to control the oil pressure.

[0049] By monitoring the back electromotive force on the two windings 14 in real time, the oil pressure is dynamically adjusted, thereby adjusting the air gap length of the motor. Valves are installed on the oil pipes on both sides. If the air gaps on both sides are not equal, resulting in unequal back electromotive forces on both sides, the valve on one side can be closed, and the oil pressure on the other side can be adjusted until the requirements are met.

[0050] When manufacturing an electric motor, a voltage test coil needs to be pre-embedded in the stator winding. The number of turns of the voltage test coil on both sides must be equal. The magnitude of the back electromotive force is determined by measuring the magnitude of the induced voltage in the voltage test coil.

[0051] Example 2:

[0052] This embodiment provides a control method for a dual-stator single-rotor permanent magnet disc motor with adjustable air gap. The permanent magnet disc motor adopts the structure described in Embodiment 1, as follows: Figure 7 and Figure 8 As shown,

[0053] When it is necessary to increase the air gap of the motor, the hydraulic pump increases the oil pressure in the guide rod hydraulic cylinder 4, pushing the guide rod 41 to move, which in turn pushes the stator back plate 12 to both sides (closer to the end cover 2), and the stator 1 also moves to both sides, thus increasing the air gap of the motor. When the increase in air gap meets the requirements, the valve closes to maintain the pressure in the guide rod hydraulic cylinder 4 and maintain the size of the motor air gap.

[0054] The voltage of the voltage test coil is detected in real time. If the voltages on both sides are not equal, the oil pressure of the hydraulic cylinder 4 on the other side is adjusted while the valve on one side is closed, and the air gap on this side is adjusted until the voltages on both sides are equal.

[0055] When it is necessary to reduce the air gap of the motor, the valves at the inlet and outlet of the guide rod hydraulic cylinder 4 are opened, allowing hydraulic oil to return to the hydraulic pump and reducing the oil pressure of the hydraulic pump. Under the action of spring 33 and axial magnetic pull, the stator back plate 12 and stator 1 move towards the rotor disk 7, thereby reducing the air gap of the motor. Similarly, the test coil voltage must be measured in real time until the test coil voltage meets the requirements. If the test coil voltages on both sides are unbalanced, the valve on one side needs to be closed first, and the oil pressure of the guide rod hydraulic cylinder 4 on the other side needs to be increased or decreased until the test coil voltages on both sides are equal.

[0056] Figure 7 and Figure 8 Middle,U c1 and U c2 These represent the voltages on the pre-embedded test coils of the stator windings on both sides, where k is the ratio of the number of series turns per phase to the number of turns of the pre-embedded coil, and U... VF n is the maximum output voltage of the frequency converter, and n is the current speed of the motor. d ξ is the target speed of the motor. ξ is a small number, generally defined according to the accuracy requirements of speed regulation or voltage regulation. U2 is the generator output voltage. ref A stable voltage value is required for the generator.

[0057] The above description is merely a specific embodiment of the present invention. Any variations that can be easily conceived by those skilled in the art within the scope disclosed in the present invention should be included within the protection scope of the invention.

Claims

1. A control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap, characterized in that, The motor includes a housing, a stator, and end covers. End covers are installed at both ends of the housing. The stator is installed on one side of the stator back plate. The stator back plate and the end covers are connected by multiple positioning guide rods. Multiple guide rod hydraulic cylinders are distributed circumferentially inside the housing. The ends of the guide rod hydraulic cylinders contact the stator back plate. The hydraulic cylinders can move the stator axially to adjust the air gap length. Control methods include: When it is necessary to increase the air gap of the motor, the hydraulic pump increases the oil pressure in the hydraulic cylinder of the guide rod, which pushes the guide rod to move, causing the stator back plate and stator to move toward the end cover side, thus increasing the air gap of the motor; when the air gap increases to meet the requirements, the valve closes. When it is necessary to reduce the air gap of the motor, open the inlet and outlet valves of the guide rod hydraulic cylinder to return the hydraulic oil to the hydraulic pump, reduce the oil pressure of the hydraulic pump, and under the action of the spring and axial magnetic pull, the stator back plate and stator move towards the rotor disk to reduce the air gap of the motor until the test coil voltage meets the requirements. If the voltages on both ends of the cover are not equal, after closing the valve on one side, adjust the oil pressure of the hydraulic cylinder on the other side of the guide rod until the voltages on both sides are equal.

2. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 1, characterized in that, The positioning guide rod is fitted with a spring, which is located between the stator back plate and the end cover.

3. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 1 or 2, characterized in that, The stator back plate has multiple first positioning holes circumferentially for installing positioning guide rods, and the end cover has multiple second positioning holes accordingly.

4. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 3, characterized in that, The positioning guide rod has a threaded section, and the second positioning hole is a threaded hole that is adapted to the threaded section of the positioning guide rod; The end of the positioning guide rod furthest from the threaded section has a polygonal head structure.

5. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 1, characterized in that, The guide rod hydraulic cylinder is fixed to the housing, and the inlet and outlet of the guide rod hydraulic cylinder are connected to conduits, which extend out of the housing.

6. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 5, characterized in that, The conduits located on the same end cap side of the housing are connected in parallel and connected to the hydraulic pump.

7. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 5, characterized in that, The conduit is fitted with a valve.

8. The control method for a dual-stator single-rotor permanent magnet motor with adjustable air gap according to claim 1, characterized in that, A rotor disk is provided between the two stators, and the rotor disk is mounted on the rotating shaft; voltage test coils are pre-embedded in the stator windings.

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