A synchronous electric device and its starting method

Abstract

This invention relates to a synchronous electric device and its starting method. The device includes at least a control component, a first rotor, and a second rotor. The first rotor has a first working winding for driving the second rotor to rotate. When the first rotor rotates to its rated speed, alternating current is applied to the first working winding, generating a rotating magnetic field. The control component sets the rotational speed of the air gap magnetic field between the first and second rotors to a minimum value. The control component adjusts the speed of the first rotor in a manner that gradually increases the rotational speed of the air gap magnetic field between the first and second rotors from its minimum value. Thus, the first rotor provides electromagnetic torque to the second rotor, synchronizing the speed of the second rotor with the rotational speed of the air gap magnetic field. This invention makes three-phase permanent magnet synchronous motors easier to start, reduces the cost of starting three-phase permanent magnet synchronous motors, and minimizes starting shock.

Description

[0001] This invention is a divisional application of the invention patent with application number 201910362159.0, application date April 30, 2019, and invention title: A Three-Phase Permanent Magnet Synchronous Motor and Its Starting Method. Technical Field

[0002] This invention relates to the field of electric motor technology, and in particular to a synchronous electric device and its starting method. Background Technology

[0003] Compared with squirrel-cage induction motors, permanent magnet synchronous motors have advantages such as higher efficiency, higher power factor, smaller size, and energy saving. Therefore, permanent magnet synchronous motors are better suited to today's society, which emphasizes conservation and environmental protection.

[0004] Permanent magnet rotors can maintain their magnetic fields without external energy, but this also makes it extremely difficult to adjust and control their magnetic fields externally, thus making it difficult for three-phase permanent magnet synchronous motors to self-start. Current technologies often utilize dedicated, high-performance frequency converters for three-phase permanent magnet synchronous motors to control the AC current in the stator windings to start the permanent magnet rotor. However, frequency converters that match the current of permanent magnet synchronous motors have high power requirements and are expensive. Existing technologies also use a method similar to a squirrel-cage device in an induction motor to asynchronously start the permanent magnet synchronous motor. However, this method results in large starting inrush currents and torques, which can easily damage the permanent magnet synchronous motor itself and downstream equipment. Summary of the Invention

[0005] This invention addresses the problems of existing technologies by providing an easy-to-start three-phase permanent magnet synchronous motor that not only has low starting cost but also low starting impact.

[0006] The present invention adopts the following technical solution: a three-phase permanent magnet synchronous motor, including a stator, a control component, and a first rotor and a second rotor, both of which are rotatably connected to the stator. The control component is used to control the rotation and braking of the first rotor. The first rotor is provided with a first working winding for driving the rotation of the second rotor. The second rotor is a permanent magnet rotor.

[0007] Preferably, the control element includes a second working winding disposed on the stator, the second working winding being used to drive the first rotor to rotate and brake the first rotor.

[0008] Preferably, the control element includes a brake and a second working winding disposed on the stator, the second working winding being used to drive the first rotor to rotate, and the brake being used to brake the first rotor.

[0009] Preferably, the brake is a hysteresis brake, an electromagnetic slip clutch, or a magnetic powder brake.

[0010] Preferably, the control unit includes a frequency converter and a second working winding disposed on the stator. The second working winding is used to drive the first rotor to rotate, and the frequency converter is used to adjust the frequency of the AC power in the second working winding.

[0011] The present invention also provides a method for starting the aforementioned three-phase permanent magnet synchronous motor, comprising the following steps performed in sequence: Step a: driving the first rotor to rotate using a control unit; Step b: after the speed of the first rotor reaches the rated value, applying alternating current to the first working winding of the first rotor, so that the speed difference between the speed of the rotating magnetic field generated by the first working winding and the speed of the first rotor is minimized, and the rotation direction of the rotating magnetic field generated by the first working winding is opposite to the rotation direction of the first rotor; Step c: using a control unit to gradually reduce the speed of the first rotor to zero and keep it stationary.

[0012] Preferably, the control element includes a second working winding disposed on the stator, the second working winding being used to drive the first rotor to rotate and brake the first rotor; in step a, alternating current is supplied to the second working winding; in step c, the supply of alternating current to the second working winding is stopped, and a direct current with a gradually increasing current value is supplied to the second working winding.

[0013] Preferably, the control component includes a brake and a second working winding disposed on the stator. The second working winding is used to drive the first rotor to rotate, and the brake is used to brake the first rotor. In step a, alternating current is supplied to the second working winding. In step c, the supply of alternating current to the second working winding is stopped, causing the braking torque of the brake to gradually increase.

[0014] Preferably, the control unit includes a frequency converter and a second working winding disposed on the stator. The second working winding is used to drive the first rotor to rotate, and the frequency converter is used to adjust the frequency of the AC current in the second working winding. In step a, AC current is supplied to the second working winding. In step c, the frequency converter is used to gradually reduce the frequency of the AC current in the second working winding.

[0015] The beneficial effects of this invention are: it makes the three-phase permanent magnet synchronous motor easier to start, reduces the cost required to start the three-phase permanent magnet synchronous motor, and minimizes the starting impact. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0018] Figure 3 This is a schematic diagram of the structure of Embodiment 3 of the present invention.

[0019] The attached figures are labeled as follows: 1. Stator; 2. Control unit; 3. First rotor; 31. First working winding; 4. Second rotor; 5. Second working winding; 6. Brake; 7. Frequency converter. Detailed Implementation

[0020] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. The present invention will be described in detail below with reference to the accompanying drawings.

[0021] Example 1

[0022] like Figure 1 As shown, a three-phase permanent magnet synchronous motor includes a stator 1, a control unit 2, and a first rotor 3 and a second rotor 4, both of which are rotatably connected to the stator 1. The control unit 2 is used to control the rotation and braking of the first rotor 3. The first rotor 3 is provided with a first working winding 31 for driving the rotation of the second rotor 4. The second rotor 4 is a permanent magnet rotor.

[0023] In a conventional three-phase permanent magnet synchronous motor, after AC current is applied to the windings of the conventional stator, the rotating magnetic field generated by the stator rotates at a relatively high speed. This means that the direction of the electromagnetic torque on the rotor changes rapidly, changing once every half cycle of the AC current. Therefore, the average torque on the rotor is zero, making starting impossible. In this embodiment, however, the rotational speed n0 of the air gap magnetic field between the first rotor 3 and the second rotor 4 is equal to the rotational speed n1 of the rotating magnetic field generated by the first working winding 31 minus the rotational speed n2 of the first rotor. The rotational speed of the air gap magnetic field between the first rotor 3 and the second rotor 4 gradually increases from its minimum value n0. The first rotor 3 can provide sufficient electromagnetic torque to the second rotor 4 so that the rotational speed of the second rotor 4 can keep up with the rotational speed of the air gap magnetic field n0. The specific workflow is as follows: The controller 2 drives the first rotor 3 to rotate. After the first rotor 3 reaches its rated speed, alternating current is applied to the first working winding 31 of the first rotor 3, causing the first working winding 31 to generate a rotating magnetic field. The speed difference between the rotating magnetic field and the first rotor 3 is minimized, and the rotation direction of the rotating magnetic field generated by the first working winding 31 is opposite to the rotation direction of the first rotor 3, effectively minimizing the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4. Subsequently, the controller 2 gradually reduces the speed of the first rotor 3, effectively increasing the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4. When the speed of the first rotor 3 decreases to zero, the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4 becomes the synchronous speed of the rotating magnetic field generated by the first working winding 31, thereby causing the speed of the second rotor 4 to gradually increase and reach the synchronous speed.

[0024] like Figure 1As shown, the control element 2 includes a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate and to brake the first rotor 3. When driving the first rotor 3 to rotate, alternating current is supplied to the second working winding 5; when it is necessary to gradually reduce the speed of the first rotor 3, direct current with a gradually increasing current value is supplied to the second working winding 5, thereby realizing the driving and braking of the first rotor 3 with a simple structure. As the most preferred embodiment, the number of poles of the first working winding 31 and the second working winding 5 are equal.

[0025] Example 2

[0026] like Figure 2 As shown, the difference between this embodiment and Embodiment 1 is that the control component 2 includes a brake 6 and a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate, and the brake 6 is used to brake the first rotor 3. When driving the first rotor 3 to rotate, alternating current is supplied to the second working winding 5; when it is necessary to gradually reduce the speed of the first rotor 3, the braking torque of the brake 6 is gradually increased, thereby realizing the control of the first rotor 3.

[0027] The braking torque of the brake 6 is adjustable. Specifically, the brake 6 is a hysteresis brake, an electromagnetic slip clutch, or a magnetic powder brake.

[0028] Example 3

[0029] like Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that the control component 2 includes a frequency converter 7 and a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate, and the frequency converter 7 is used to adjust the frequency of the AC power in the second working winding 5. Since the frequency converter 7 is used to drive the first rotor 3 rather than the second rotor 4 connected to the load, the required power is smaller, and a common frequency converter can be used.

[0030] Example 4

[0031] This embodiment provides a method for starting the three-phase permanent magnet synchronous motor described in Embodiment 1, characterized by the following steps performed sequentially: Step a: using the control unit 2 to drive the first rotor 3 to rotate; Step b: after the speed of the first rotor 3 reaches the rated value, AC current is applied to the first working winding 31 of the first rotor 3, so that the speed difference between the speed of the rotating magnetic field generated by the first working winding 31 and the speed of the first rotor 3 is minimized, and the rotation direction of the rotating magnetic field generated by the first working winding 31 is opposite to the rotation direction of the first rotor 3; Step c: using the control unit 2 to gradually reduce the speed of the first rotor 3 to zero and keep it stationary.

[0032] The minimum speed difference between the rotating magnetic field generated by the first working winding 31 and the speed of the first rotor 3 is equivalent to minimizing the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4. By using the control unit 2 to gradually reduce the speed of the first rotor 3 to zero, it is equivalent to gradually increasing the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4. The first rotor 3 can provide sufficient electromagnetic torque to the second rotor 4 so that the speed of the second rotor 4 can keep up with the speed of the air gap magnetic field. When the speed of the first rotor 3 decreases to zero, the speed of the air gap magnetic field between the first rotor 3 and the second rotor 4 is the synchronous speed of the rotating magnetic field generated by the first working winding 31, thereby realizing the starting of the three-phase permanent magnet synchronous motor.

[0033] Example 5

[0034] The difference between this embodiment and embodiment four is that the control component 2 includes a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate and brake the first rotor 3. In step a, alternating current is supplied to the second working winding 5. In step c, the supply of alternating current to the second working winding 5 is stopped, and direct current with a gradually increasing current value is supplied to the second working winding 5. The alternating current causes the second working winding 5 to generate a rotating magnetic field and drive the first rotor 3 to rotate. The direct current causes the second working winding 5 to generate a stationary magnetic field. The stationary magnetic field generates a braking torque on the first rotor 3, causing the first rotor 3 to decelerate. The larger the current value, the greater the braking torque of the stationary magnetic field on the first rotor 3, thereby achieving the effect of gradually reducing the speed of the first rotor 3.

[0035] Example 6

[0036] The difference between this embodiment and embodiment four is that the control component 2 includes a brake 6 and a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate, and the brake 6 is used to brake the first rotor 3. In step a, alternating current is supplied to the second working winding 5; in step c, the supply of alternating current to the second working winding 5 is stopped, causing the braking torque of the brake 6 to gradually increase. The alternating current causes the second working winding 5 to generate a rotating magnetic field and drive the first rotor 3 to rotate. The gradually increasing braking torque of the brake 6 causes the first rotor 3 to gradually decelerate.

[0037] Example 7

[0038] The difference between this embodiment and embodiment four is that the control component 2 includes a frequency converter 7 and a second working winding 5 disposed on the stator 1. The second working winding 5 is used to drive the first rotor 3 to rotate, and the frequency converter 7 is used to adjust the frequency of the AC current in the second working winding 5. In step a, AC current is supplied to the second working winding 5. In step c, the frequency converter 7 is used to gradually reduce the frequency of the AC current in the second working winding 5. The AC current causes the second working winding 5 to generate a rotating magnetic field and drive the first rotor 3 to rotate. As the frequency of the AC current in the second working winding 5 gradually decreases, the rotational speed of the rotating magnetic field in the second working winding 5 also gradually decreases, thereby causing the rotational speed of the first rotor 3 to gradually decrease.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A synchronous electric device, characterized in that, It includes at least a control element (2), a first rotor (3) and a second rotor (4), wherein the first rotor (3) is provided with a first working winding (31) for driving the second rotor (4) to rotate. When the first rotor (3) rotates to its rated speed, alternating current is applied to the first working winding (31) and a rotating magnetic field is generated. The control unit (2) sets the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) to a minimum value. The control unit (2) adjusts the rotational speed of the first rotor (3) in such a way that the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) gradually increases from the minimum value, so that the first rotor (3) provides electromagnetic torque to the second rotor (4) so ​​that the rotational speed of the second rotor (4) is synchronized with the rotational speed of the air gap magnetic field. The control method by which the control element (2) minimizes the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) includes at least the following: The speed difference between the rotational speed of the rotating magnetic field generated by the first working winding (31) and the rotational speed of the first rotor (3) is minimized, and the rotational direction of the rotating magnetic field is opposite to the rotational direction of the first rotor (3). The control method by which the control element (2) adjusts the rotational speed of the first rotor (3) in such a way as to gradually increase the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) from a minimum value includes at least the following: Let the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) be the minimum value. The rotational speed of the first rotor (3) is gradually reduced, and the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) is gradually increased; The control unit (2) causes the rotational speed of the first rotor (3) to gradually decrease to zero and remain stationary. At this time, the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) is synchronized with the rotational speed of the rotating magnetic field generated by the first working winding (31). The rotational speed of the second rotor (4) gradually increases and reaches the synchronous speed.

2. The synchronous electric device according to claim 1, characterized in that, The device further includes a second working winding (5), which is used to drive the first rotor (3) to rotate and brake the first rotor (3). When driving the first rotor (3) to rotate, the control unit (2) supplies alternating current to the second working winding (5); When the first rotor (3) is gradually slowed down, the control unit (2) stops supplying AC power to the second working winding (5) and supplies DC power with a gradually increasing current value to the second working winding (5).

3. The synchronous electric device according to claim 1 or 2, characterized in that, The device also includes a brake (6). When the first rotor (3) is gradually decelerated, the control unit (2) causes the braking torque of the brake (6) to gradually increase, thereby achieving control of the first rotor (3).

4. The synchronous electric device according to claim 1 or 2, characterized in that, The device also includes a frequency converter (7) for adjusting the frequency of the AC power in the second working winding (5); When the control unit (2) gradually reduces the speed of the first rotor (3) to zero and keeps it stationary, the control unit (2) uses the frequency converter (7) to gradually reduce the frequency of the alternating current in the second working winding (5).

5. A starting method for a synchronous electric device, characterized in that, The method includes at least: When the first rotor (3) rotates to its rated speed, alternating current is applied to the first working winding (31) and a rotating magnetic field is generated. The control unit (2) sets the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) to a minimum value. The control unit (2) adjusts the rotational speed of the first rotor (3) in such a way that the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) gradually increases from the minimum value, so that the first rotor (3) provides electromagnetic torque to the second rotor (4) so ​​that the rotational speed of the second rotor (4) is synchronized with the rotational speed of the air gap magnetic field. The control method by which the control element (2) minimizes the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) includes at least the following: The speed difference between the rotational speed of the rotating magnetic field generated by the first working winding (31) and the rotational speed of the first rotor (3) is minimized, and the rotational direction of the rotating magnetic field is opposite to the rotational direction of the first rotor (3). The control method by which the control element (2) adjusts the rotational speed of the first rotor (3) in such a way as to gradually increase the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) from a minimum value includes at least the following: Let the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) be the minimum value. The rotational speed of the first rotor (3) is gradually reduced, and the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) is gradually increased; The control unit (2) causes the rotational speed of the first rotor (3) to gradually decrease to zero and remain stationary. At this time, the rotational speed of the air gap magnetic field between the first rotor (3) and the second rotor (4) is synchronized with the rotational speed of the rotating magnetic field generated by the first working winding (31). The rotational speed of the second rotor (4) gradually increases and reaches the synchronous speed.

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