Double-squirrel-cage permanent magnet motor of fractional slot concentrated winding and pole-changing switching method

Abstract

The invention provides a double-squirrel-cage permanent magnet motor with a fractional slot concentrated winding and a pole-changing switching method, the motor comprises a stator and a rotor, the stator comprises a stator winding design and a winding pole-changing switching method, and two groups of conducting bars are arranged on the outer circumferential side of the rotor. The two groups of conducting bars are respectively connected with the two end rings to form two independent double-squirrel-cage structures, and each conducting bar corresponds to a permanent magnet steel magnetic pole distributed in the circumferential direction of the rotor. Two groups of conducting bars are arranged on the outer side of the rotor, and the two groups of conducting bars are respectively connected with the two end rings to form two independent double-squirrel-cage structures. The independent double-squirrel-cage structure not only can filter specific-order magnetomotive force harmonics generated by a stator winding, but also greatly reduces the magnetic leakage phenomenon due to the position relation between the conducting bars and the magnetic poles of the permanent magnets, so that the blocking effect of the conducting bars on a permanent magnetic circuit is reduced to the minimum, the utilization rate of the permanent magnets is improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field related to permanent magnet motors, and in particular relates to a double-squirrel cage permanent magnet motor with fractional slot concentrated windings and a pole changing switching method. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The fractional slot concentrated winding and its system have become a research hotspot in recent years due to their unique advantages. Compared with the traditional integer slot winding motor, the fractional slot winding motor has the following outstanding advantages: the fractional slot concentrated winding has short ends, which is conducive to stator wire embedding and reducing copper consumption, effectively reducing winding copper loss and improving motor efficiency; and the ends do not overlap, reducing phase coupling, making it have better fault tolerance. However, the fractional slot concentrated winding is only well applied in permanent magnet synchronous motors. Such motors cannot achieve self-starting and usually need to be equipped with a frequency converter, which increases the cost of use. In addition, the fractional slot concentrated winding will generate a rich magnetomotive force harmonics. In the cage-type asynchronous start permanent magnet motor, these harmonics will cause the rotor bars to generate a rich frequency induced current. Traditional asynchronous start permanent magnet synchronous motors all use integer slot windings, usually with an integer of 2 or 3 slots per pole per phase, which means that a three-phase 8-pole motor requires at least 48 stator slots. If the motor size is small, the slot utilization rate will be reduced, wire embedding will be difficult, and it will also be unfavorable for die manufacturing.

[0004] The cage-type asynchronous start permanent magnet synchronous motor is a type of permanent magnet synchronous motor with self-starting capability. Its starting depends on the asynchronous torque generated by the interaction between the stator rotating magnetic field and the rotor bars. Compared with traditional electrically excited asynchronous motors, it has the advantages of high power factor and high power density, and is widely used in many fields. For example, patent CN210536478U discloses a dual-stator asynchronous starting permanent magnet synchronous motor core structure, a plurality of rotor starting cage bars are arranged on the outer ring surface of the rotor core, the rotor starting cage bars are double cage bars, a plurality of rotor magnetic steel slot groups are arranged on the inner ring surface of the rotor core, the rotor magnetic steel slot group is composed of two rotor magnetic steel slots arranged in a V-shape, but in this patent all the guide bars are connected without grouping to form a cage shape, which is two inner and outer cages in shape, but these two cages are interconnected and not independent, and these guide bars are closely arranged on the outer circumference of the rotor, which is not conducive to the permanent magnet magnetic lines of force passing through the air gap to reach the stator, and there is a leakage magnetic phenomenon. The rotor described in this patent is adaptive to integer slot windings and is no longer applicable to fractional slot winding motors. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a double-cage permanent magnet motor with fractional slot concentrated winding and a pole-changing switching method. The fractional slot concentrated winding is applied to the asynchronous starting permanent magnet synchronous motor so that the motor does not need to be matched with a frequency converter, can realize self-starting, and reduce the use cost; and for motors with a large number of poles, a series of process problems caused by too many stator slots are avoided. At the same time, in order to suppress the large motor induced in the rotor bars by the abundant magnetomotive force harmonics of the fractional slot concentrated winding, the motor rotor bars are specially connected to form two independent cage structures, that is, a double-cage rotor structure, which can not only filter out the specific magnetomotive force harmonics generated by the stator winding, but also avoid the large induced current in the bars, improve the motor efficiency, optimize the output torque, and reduce the unsafe factors in production and use. In addition, the relative position between the bars and the permanent magnet poles is designed, which not only greatly reduces the magnetic leakage phenomenon, but also improves the utilization rate of the permanent magnet. Finally, during the motor startup process, when the rotor speed reaches the synchronous speed for the first time, the stator winding pole-changing switching is performed to complete the transition from the starting stage to the synchronous operation stage.

[0006] This embodiment provides an asynchronous start permanent magnet synchronous motor with a double squirrel cage structure of a fractional slot concentrated winding, the motor comprising a stator and a rotor, characterized in that the stator comprises a stator winding design and a winding switching method, and the rotor comprises a rotor bar connection method and a relative number and position relationship between permanent magnets and the bars. Two groups of bars are arranged on the outer circumference of the rotor, and the two groups of bars are respectively connected to two end rings to form two independent squirrel cage structures, and each bar corresponds to a permanent magnet steel arranged in the circumferential direction of the rotor.

[0007] Furthermore, the plurality of conductive bars are divided into two groups at intervals and are evenly distributed on the outer side of the rotor.

[0008] Furthermore, the conductive bars in different groups are adjacent to each other and are evenly spaced apart and distributed on the outer side of the rotor.

[0009] Furthermore, a plurality of permanent magnets are evenly distributed on the circumferential direction of the rotor, and the permanent magnets are arranged in a V-shape.

[0010] Furthermore, each V-shaped arrangement of permanent magnet steel corresponds to a conductive bar.

[0011] Furthermore, the permanent magnets are distributed in an internal manner and are separated from the air gap by only a magnetic bridge.

[0012] Furthermore, the stator adopts a three-phase fractional-slot concentrated winding.

[0013] Furthermore, each of the conductive bars on the rotor end surface is located between two adjacent V-shaped arranged permanent magnets.

[0014] Furthermore, the V-shaped arrangement of the permanent magnet steel has a V-angle facing one side of the rotor;

[0015] Alternatively, each group of guide bars is connected by two end rings to form a cage structure, and the two end rings constituting the same cage differ in axial direction only by the axial length of a guide bar; the end rings constituting different cages are mutually deflected by a certain angle around the axis.

[0016] The present invention also provides a pole-changing starting switching method for an asynchronous starting permanent magnet synchronous motor with a double-cage structure, comprising: during the motor starting process, when the rotor speed reaches the synchronous speed for the first time, winding switching is performed, the winding before switching is a 12-slot 4-pole winding, and the winding after switching is a 12-slot 8-pole winding; the 12 coils of the 12-slot 4-pole winding are reversed every other coil and the phase sequence of two phases is arbitrarily exchanged to obtain a 12-slot 8-pole winding.

[0017] One or more of the above technical solutions have the following beneficial effects:

[0018] In the present invention, fractional slot concentrated winding is applied to asynchronous starting permanent magnet synchronous motor without frequency converter, which can realize self-starting, reduce use cost, realize the design of few slots and multiple poles of this type of motor, and enrich the application occasions of this type of motor; two groups of bars are arranged on the outer side of the rotor, and the two groups of bars are respectively connected with two end rings to form two independent cages. The double cage structure can not only filter out the specific sub-magnetic harmonics generated by the stator winding, but also the position relationship between the bars and the permanent magnet poles not only greatly reduces the leakage phenomenon, but also improves the utilization rate of the permanent magnet; before the winding switching, the 12-slot 4-pole winding has a good starting ability, which can increase the motor speed to the synchronous speed in a short time. After the winding switching is completed, the large induced current in the rotor bars before the winding switching will quickly decay into a small-amplitude harmonic current, and continue to maintain a small amplitude after entering the synchronous operation state, which not only minimizes the influence of the rotor bars on the synchronous operation, but also improves the safety performance of the motor, so that the motor has a good steady-state operation ability.

[0019] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings in the specification which constitute a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation on the present invention. The motor parameters can be arbitrarily selected and modified accordingly under the premise of complying with the design rules.

[0021] Figure 1 A cross-sectional view of an asynchronous starting permanent magnet synchronous motor with a double squirrel cage structure in Embodiment 1 of the present invention;

[0022] Figure 2 This is a magnetic field distribution diagram of an asynchronous starting permanent magnet synchronous motor with a double squirrel cage structure in Embodiment 1 of the present invention;

[0023] Figure 3 It is a perspective view of the mutually independent double squirrel cage structure formed in the first embodiment of the present invention;

[0024] Figure 4 It is a front view of the mutually independent double squirrel cage structure formed in the first embodiment of the present invention;

[0025] Figure 5 A side view of a mutually independent double squirrel cage structure formed in the first embodiment of the present invention;

[0026] Figure 6 This is a phase diagram of a 12-slot 8-pole winding of a fractional-slot concentrated winding asynchronous start permanent magnet synchronous motor after winding switching in Embodiment 2 of the present invention;

[0027] Figure 7 This is a connection diagram of 12-slot 8-pole winding coils after winding switching of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor in the second embodiment of the present invention.

[0028] Figure 8 This is a phase diagram of a 12-slot 4-pole winding of a fractional-slot concentrated winding asynchronous start permanent magnet synchronous motor before winding switching in the second embodiment of the present invention;

[0029] Fig. 9 This is a connection diagram of 12-slot 4-pole winding coils before winding switching of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor in the second embodiment of the present invention.

[0030] In the figure, 1. stator teeth, 2. stator, 3. stator winding, 4. permanent magnet, 5. guide bar, 6. magnetic bridge, 7. rotor, 8. end ring. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0032] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0033] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0034] Embodiment 1

[0035] like Figure 1-Figure 2As shown, this embodiment discloses an asynchronous starting permanent magnet synchronous motor with a double squirrel cage structure, wherein two groups of guide bars 5 are arranged on the outer circumferential side of the rotor 7, and the two groups of guide bars 5 are respectively connected to the two end rings 8 to form two independent squirrel cage structures, and each guide bar 5 corresponds to a permanent magnet magnetic pole distributed in the circumferential direction of the rotor 7.

[0036] Figure 3-Figure 5 It is only used to show the group connection method of the conductor bar and does not represent the specific shape of the conductor bar. In this embodiment, a plurality of conductor bars 5 are arranged on the outer side of the rotor 7 along the circumferential direction. The plurality of conductor bars 5 are annular and evenly and equidistantly distributed on the outer side of the rotor 7, and are connected in groups to form a double squirrel cage structure to filter out specific harmonics.

[0037] The rotor 7 has an overall cylindrical structure, and a plurality of conductive bars 5 are evenly and equidistantly distributed on the outer side along the circumferential direction. The conductive bars 5 are divided into two groups, and the grouping method is as follows: any conductive bar 5 is in a different group from the two adjacent conductive bars 5 on its left and right sides. The two groups of conductive bars 5 are respectively connected through end rings 8 to form two independent cages. The conductive bars 5 constituting any cage are still evenly and equidistantly distributed on the circumference. Since there is no contact or connection between the two cages, they are independent of each other.

[0038] Figure 2 : is a magnetic field distribution diagram of an asynchronous starting permanent magnet synchronous motor with a double squirrel cage structure in this embodiment, and the arrow is the magnetization direction of the permanent magnet.

[0039] Specifically, in this embodiment, 8 guide bars 5 are provided, and the pitch angle between them is 45°. These guide bars 5 are divided into two groups, and the grouping method is: any guide bar 5 and the two adjacent guide bars 5 on its left and right sides are in different groups, such as Figure 3 As shown, a group of conductor bars 5 needs an end ring 8 at both ends to form a closed loop and connect to form a cage, so two groups of conductor bars 5 need a total of four end rings 8 to form two independent cages. The conductor bars 5 constituting any cage are still evenly and equidistantly distributed on the circumference, and the pitch angle between the conductor bars 5 from the same cage is 90°. Figure 4 , Figure 5 As shown, the two end rings 8 constituting the same squirrel cage differ only by a distance in the axial direction, which is the axial length of the guide bar 5; the end rings of different squirrel cages not only have a difference in the axial direction, but also deflect from each other around the axis by an angle, which is equal to the pitch angle between adjacent guide bars 5 of 45°.

[0040] In this embodiment, a plurality of permanent magnets are evenly distributed in the circumferential direction of the rotor, and the permanent magnets are arranged in a V-shape. Each pole permanent magnet corresponds to one conductive bar 5, and their positional relationship is that from the rotor end face, the geometric symmetry axis of each pole permanent magnet completely coincides with the geometric symmetry axis of the conductive bar 5 corresponding to it, and such a positional relationship minimizes the negative impact of the conductive bar 5 on the permanent magnetic circuit, and the magnetic lines of force can enter the stator more easily.

[0041] The permanent magnets are arranged in an internal manner and are separated from the air gap by only a magnetic bridge, so the magnetic lines of force can more easily enter the stator and return to the rotor to form a loop. The openings of the permanent magnets arranged in a V-shape face outwards.

[0042] In this embodiment, the overall structure of the stator 2 is cylindrical, and slots are evenly and equidistantly opened on the inner side along the circumferential direction, with a pitch angle of 30°. Double-layer fractional slot concentrated windings are placed in the slots, that is, two element edges are placed in each slot, and the element edges of two adjacent slots are closed to form a coil wound on the middle stator tooth. Compared with single-layer windings, double-layer windings can double the number of coils, and fractional slot concentrated windings minimize the coil ends. Specifically, there are 12 coil groups in total, 4 coil groups per phase.

[0043] The stator winding adopts concentrated winding. The conductors of two adjacent slots are closed to form a coil wound on the middle stator tooth 1. The coil end is short, copper is saved, copper consumption is low, efficiency and power density can be improved, and cost can be saved.

[0044] The stator adopts fractional slot winding, and the number of slots per pole per phase is a true fraction less than 1. Compared with integer slot motors, when the number of poles and phases are the same, the number of stator slots is less. Taking a three-phase 8-pole 12-slot motor as an example, the number of slots per pole per phase is 1 / 2, which is a true fraction less than 1. Compared with integer slot motors, when the number of poles and phases are the same, the number of stator slots is less.

[0045] The application of fractional-slot concentrated winding and double squirrel-cage structure to the asynchronous-start permanent-magnet synchronous motor proposed in this embodiment not only ensures that the stator winding is a fractional-slot concentrated winding, but also belongs to an asynchronous-start permanent-magnet synchronous motor; it not only reduces winding losses, improves motor efficiency, and responds to energy saving, but also does not require a frequency converter and can achieve self-starting; it not only saves material costs, but also reduces system costs.

[0046] Embodiment 2

[0047] This embodiment provides a pole-changing switching method for a double-squirrel-cage permanent magnet motor with fractional-slot concentrated windings, comprising:

[0048] The stator winding is directly connected to the industrial frequency three-phase AC power supply. The stator generates a rotating magnetic field, which generates an induced current in the rotor cage winding, and then generates a rotor rotating magnetic field. The stator and rotor magnetic fields interact with each other to generate asynchronous torque, which accelerates the rotor. When the rotor accelerates to the synchronous speed, the winding is switched. After the switching, no large induced current is generated in the rotor winding. At this time, there is only the magnetic field generated by the permanent magnet on the rotor, realizing the asynchronous starting of the permanent magnet synchronous motor.

[0049] During the motor startup process, when the rotor speed reaches the synchronous speed corresponding to the second polarity for the first time, the winding is switched. All coils in the stator slots are used before and after the switching, and only the connection method between the coils is changed. Figure 8-9 As shown, the winding before switching is a three-phase 12-slot 4-pole winding, its unit motor number is 2, and the winding arrangement is cycled every 6 slots; Figure 6-7 As shown in the figure, the switched winding is a three-phase 12-slot 8-pole winding, the number of its unit motors is 4, and the winding arrangement is cycled every 3 slots. Figure 6 , 8 As shown, by reversing the connection of every other coil of the 12-slot 4-pole winding and arbitrarily exchanging the phase sequence of two phases, a 12-slot 8-pole winding can be obtained. The specific sub-magnetic harmonics generated by the 12-slot 8-pole winding can be suppressed by the aforementioned double-cage structure, and no large induced current will be generated in the rotor bars, so that the motor has better synchronous operation capability.

[0050] During the starting process of the motor, the stator winding connection is switched. The magnetomotive force working harmonics generated by the stator winding are different before and after the switching. The magnetomotive force generated by the stator winding before the switching enables the motor to have a stronger starting ability, and also induces a large current in the rotor bars; the stator winding after the switching can make the motor work in a synchronous state, and there is no large induced current in the rotor bars.

[0051] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A double squirrel cage permanent magnet motor with fractional slot concentrated winding, characterized in that: The motor includes a stator and a rotor, wherein the stator includes a stator winding design and a winding switching method, and the rotor includes a rotor bar connection method and a relative number and position relationship between permanent magnets and the bars. Two groups of bars are arranged on the outer circumference of the rotor, and the two groups of bars are respectively connected to different end rings to form two independent squirrel cage structures, and each bar corresponds to a permanent magnet pole distributed in the circumferential direction of the rotor.

2. A double-squirrel cage permanent magnet motor with fractional slot concentrated windings as claimed in claim 1, characterized in that: The plurality of guide bars are divided into two groups at intervals and are evenly distributed on the outer side of the rotor.

3. The double-squirrel cage permanent magnet motor with fractional slot concentrated winding according to claim 1, characterized in that: The conductive bars in different groups are adjacent to each other and are evenly spaced apart and distributed on the outer side of the rotor.

4. A double-squirrel cage permanent magnet motor with fractional slot concentrated windings as claimed in claim 1, characterized in that: A plurality of permanent magnets are evenly distributed on the rotor in a circumferential direction thereof, and the permanent magnets are arranged in a V shape.

5. A double-squirrel cage permanent magnet motor with fractional slot concentrated windings as claimed in claim 4, characterized in that: Each V-shaped permanent magnet corresponds to a conductive bar.

6. A double-squirrel cage permanent magnet motor with fractional slot concentrated windings as claimed in claim 4, characterized in that: The permanent magnets are distributed in an internal manner and are separated from the air gap by only a magnetic bridge.

7. The double-squirrel cage permanent magnet motor with fractional slot concentrated winding according to claim 1, characterized in that: The stator adopts a three-phase fractional slot concentrated winding.

8. The double-squirrel cage permanent magnet motor with fractional slot concentrated winding according to claim 1, characterized in that: On the rotor end surface, each guide bar is located between two adjacent V-shaped arranged permanent magnets.

9. The double-squirrel cage permanent magnet motor with fractional slot concentrated winding according to claim 1, characterized in that: The V-shaped permanent magnets have a V-angle facing one side of the rotor; Alternatively, each group of guide bars is connected by two end rings to form a cage structure, and the two end rings constituting the same cage differ in axial direction only by the axial length of a guide bar; the end rings constituting different cages are mutually deflected by a certain angle around the axis.

10. A switching method for a double-squirrel cage permanent magnet motor with fractional slot concentrated windings, characterized in that: During the motor startup process, when the rotor speed reaches the synchronous speed for the first time, the winding is switched. The winding before the switch is a 12-slot 4-pole winding, and the winding after the switch is a 12-slot 8-pole winding; The 12 coils of the 12-slot 4-pole winding are reversely connected one by one and the phase sequence of the two phases is arbitrarily exchanged to obtain a 12-slot 8-pole winding.

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