Fractional-slot concentrated winding double squirrel cage permanent magnet motor and variable pole switching method

Abstract

The application provides a fractional-slot concentrated winding double-cage permanent magnet motor and a variable-pole switching method. The motor comprises a stator and a rotor. The stator comprises a stator winding design and a winding variable-pole switching method. Two groups of conducting bars are arranged on the outer circumferential side of the rotor. The two groups of conducting bars are connected with two end rings respectively to form two independent double-cage structures. Each conducting bar is arranged corresponding to a permanent magnet magnetic pole distributed in the circumferential direction of the rotor. Two groups of conducting bars are arranged on the outer side of the rotor. The two groups of conducting bars are connected with two end rings respectively to form two independent double-cage structures. The independent double-cage structure can not only filter specific harmonic magnetic motive force generated by the stator winding, but also greatly reduce the magnetic leakage phenomenon between the conducting bar and the permanent magnet magnetic pole, so that the blocking effect of the conducting bar on the permanent magnet magnetic circuit is reduced to the minimum, the utilization rate of the permanent magnet is improved, and the cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of permanent magnet motors, and particularly relates to a fractional-slot concentrated winding double-cage permanent magnet motor and a variable-pole switching method. BACKGROUND

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

[0003] Fractional-slot concentrated winding and its system have become a research hotspot in recent years due to its unique advantages. Compared with the traditional integer-slot winding motor, the fractional-slot concentrated winding motor has the following outstanding advantages: the end of the fractional-slot concentrated winding is short, which is conducive to stator wire embedding and reduces the amount of copper, effectively reduces the copper loss of the winding, and improves the efficiency of the motor; and the end is not overlapped, which reduces the inter-phase coupling and makes it have better fault tolerance. However, the fractional-slot concentrated winding is only well applied in permanent magnet synchronous motors, and such motors cannot realize self-starting and usually need to be matched with a frequency converter, which increases the use cost. In addition, the fractional-slot concentrated winding generates rich magnetic potential harmonics, and in a cage asynchronous starting permanent magnet synchronous motor, these harmonics will cause the induction current with rich frequency in the rotor bar. The traditional asynchronous starting permanent magnet synchronous motor adopts an integer-slot winding, and the number of slots per pole per phase is usually an integer of 2 or 3, which means that a three-phase 8-pole motor needs at least 48 stator slots. If the motor size is small, the slot utilization rate will be reduced, the wire embedding will be difficult, and the manufacturing of the punching die will also be not conducive.

[0004] The cage asynchronous starting permanent magnet synchronous motor is a kind of permanent magnet synchronous motor with self-starting capability, and its starting relies on the asynchronous torque generated by the interaction of the stator rotating magnetic field and the rotor bar. Compared with the traditional electrically excited asynchronous motor, 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 double-stator asynchronous starting permanent magnet synchronous motor core structure, a plurality of rotor starting squirrel cage bars are arranged on the outer ring surface of the rotor core, the rotor starting squirrel cage bars are double squirrel cage bars, a plurality of rotor magnet steel groove groups are arranged on the inner ring surface of the rotor core, and each rotor magnet steel groove group is composed of two V-shaped rotor magnet steel grooves. However, in the patent, all the bars are connected to form a shape of a squirrel cage without grouping, and the shape is an inner and outer squirrel cage, but the two squirrel cages are connected to each other and are not independent, and the bars are arranged closely on the outer circumference of the rotor, which is not conducive to the magnetic flux of the permanent magnet passing through the air gap to reach the stator, and there is a magnetic leakage phenomenon. The rotor in the patent is adapted to an integer-slot winding, and is not applicable to a fractional-slot winding motor. SUMMARY

[0005] In order to overcome the above-mentioned deficiencies of the prior art, the application provides a fractional-slot concentrated winding double-cage permanent magnet motor and a variable-pole switching method. The fractional-slot concentrated winding is applied to an asynchronous starting permanent magnet synchronous motor, so that the motor can realize self-starting without a frequency converter, and the use cost is reduced. For a motor with a large number of poles, a series of process problems caused by too many stator slots are avoided. In order to suppress the large motor induced in the rotor bar by the rich magnetic motive force harmonics of the fractional-slot concentrated winding, the rotor bar is connected in a special way to form two independent squirrel cage structures, i.e. a double squirrel cage rotor structure. The double squirrel cage rotor structure can filter out the specific magnetic motive force harmonics generated by the stator winding, avoid large induced current in the bar, improve the motor efficiency, optimize the output torque, and reduce the unsafe factors in production and use. In addition, the relative position between the bar and the permanent magnet magnetic pole 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 starting process, when the rotor speed reaches the synchronous speed for the first time, the stator winding variable-pole switching is performed to complete the transition from the starting stage to the synchronous running stage.

[0006] The embodiment provides an asynchronous starting permanent magnet synchronous motor with a fractional-slot concentrated winding double squirrel cage structure, 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 mode and a relative number and position relationship between a permanent magnet and a bar. Two groups of bars are arranged on the outer circumference of the rotor, and the two groups of bars are connected with two end rings to form two independent squirrel cage structures, and each bar corresponds to a permanent magnet arranged in the circumferential direction of the rotor.

[0007] Further, the plurality of bars are divided into two groups with an interval, and are evenly distributed on the outer side of the rotor.

[0008] Further, the bars in different groups are adjacent and evenly distributed on the outer side of the rotor.

[0009] Further, 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.

[0010] Further, each V-shaped arranged permanent magnet corresponds to a bar.

[0011] Further, the permanent magnet is arranged in a built-in manner, and is separated from the air gap only by a magnetic bridge.

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

[0013] Further, each bar is located between adjacent two V-shaped arranged permanent magnets on the end face of the rotor.

[0014] Further, the V-shaped permanent magnet steel is arranged in a V-shaped angle towards the rotor side.

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

[0016] The application further provides a variable-pole starting switching method for the double-squirrel-cage-structure asynchronous starting permanent magnet synchronous motor, comprising the following steps: during the motor starting process, when the rotating speed of the rotor reaches the synchronous speed for the first time, the winding switching is performed, the winding before the switching is a 12-slot 4-pole winding, and the winding after the switching is a 12-slot 8-pole winding; the 12 coils of the 12-slot 4-pole winding are reversely connected in groups with an interval and the phase sequence of two phases is exchanged at random to obtain the 12-slot 8-pole winding.

[0017] The above one or more technical solutions have the following beneficial effects:

[0018] In the application, the fractional-slot concentrated winding is applied to the asynchronous starting permanent magnet synchronous motor without being matched with a frequency converter, so that self-starting can be realized, the use cost is reduced, the few-slot and multi-pole design of the motor is realized, and the application occasions of the motor are enriched; two groups of conductive bars are arranged outside the rotor, and the two groups of conductive bars are connected with two end rings to form two independent squirrel cages. The double-squirrel-cage structure can not only filter specific magnetic motive force harmonic waves generated by the stator winding, but also greatly reduce the magnetic leakage phenomenon and improve the utilization rate of the permanent magnet. Before the winding switching, the 12-slot 4-pole winding has good starting capability and can make the rotating speed of the motor increase to the synchronous speed in a short time. After the winding switching, the large amplitude induced current of the rotor conductive bar before the winding switching is rapidly attenuated to a small amplitude harmonic current, and the small amplitude is continuously maintained after the synchronous running state is entered. This not only minimizes the influence of the rotor conductive bar on the synchronous running, but also improves the safety performance of the motor, so that the motor has good steady-state running capability.

[0019] The advantages of the additional aspects of the application will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings accompanying the specification of the application serve to provide a further understanding of the application, the illustrative embodiments of the application and the description thereof serve to explain the application, and do not constitute an improper limitation of the application. The motor parameters can be arbitrarily selected and changed under the premise of meeting the design rules.

[0021] Figure 1 FIG. 1 is a cross-sectional view of a double-squirrel-cage-structure asynchronous starting permanent magnet synchronous motor according to an embodiment of the application;

[0022] Figure 2 A magnetic field distribution diagram of a double squirrel cage structure asynchronous starting permanent magnet synchronous motor in the embodiment one of the present application;

[0023] Figure 3 A perspective view of the mutually independent double squirrel cage structure formed in the embodiment one of the present application;

[0024] Figure 4 A front view of the mutually independent double squirrel cage structure formed in the embodiment one of the present application;

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

[0026] Figure 6 A 12-slot 8-pole winding distribution diagram of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor after winding switching in the embodiment two of the present application;

[0027] Figure 7 A 12-slot 8-pole winding connection diagram of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor after winding switching in the embodiment two of the present application.

[0028] Figure 8 A 12-slot 4-pole winding distribution diagram of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor before winding switching in the embodiment two of the present application;

[0029] Figure 9 A 12-slot 4-pole winding connection diagram of the fractional-slot concentrated winding asynchronous starting permanent magnet synchronous motor before winding switching in the embodiment two of the present application.

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

[0031] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0032] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments consistent with the present application.

[0033] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0034] Embodiment one

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

[0036] Figures 3-5 Only the grouping connection mode of the bars is shown, which does not represent the specific shape of the bars. In the embodiment, a plurality of bars 5 are arranged on the outer side of the rotor 7 in the circumferential direction, the plurality of bars 5 are annular and uniformly and equidistantly distributed on the outer side of the rotor 7, and form a double squirrel cage structure through grouping connection to filter out specific harmonics.

[0037] The overall structure of the rotor 7 is cylindrical, and a plurality of bars 5 are uniformly and equidistantly distributed on the outer side in the circumferential direction. The bars 5 are divided into two groups, and the grouping mode is that any bar 5 and the two bars 5 adjacent to it on the left and right sides are in different groups. The two groups of bars 5 are respectively connected through the end rings 8 to form two independent squirrel cages, and the bars 5 constituting any squirrel cage still maintain uniform and equidistant distribution in the circumferential direction. Because there is no contact or connection between the two squirrel cages, they are independent of each other.

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

[0039] Specifically, in the embodiment, there are 8 bars 5, and the pitch angle between the bars 5 is 45°. The bars 5 are divided into two groups, and the grouping mode is that any bar 5 and the two bars 5 adjacent to it on the left and right sides are in different groups, as shown in Figure 3 As shown, one end ring 8 is needed at the front and rear ends of one group of bars 5 to form a closed loop and connect to form a squirrel cage. Therefore, two groups of bars 5 need four end rings 8 to form two independent squirrel cages. The bars 5 constituting any squirrel cage still maintain uniform and equidistant distribution in the circumferential direction, and the pitch angle between the bars 5 from the same squirrel cage is 90°. As shown in Figure 4 、 Figure 5 As shown, the two end rings 8 constituting the same squirrel cage only differ by a distance in the axial direction, and the distance is the axial length of the bar 5. The end rings of different squirrel cages not only have a difference in the axial direction, but also are deflected by an angle around the shaft, and the angle is equal to the pitch angle 45° between the adjacent bars 5.

[0040] In the embodiment, the rotor is uniformly distributed with a plurality of permanent magnet steels in the circumferential direction thereof, and the permanent magnet steels are arranged in a V shape. Each permanent magnet of each pole corresponds to one of the conductive bars 5, and the geometric symmetry axis of each permanent magnet of each pole is completely coincident with the geometric symmetry axis of the corresponding conductive bar 5 from the end surface of the rotor. Such a positional relationship minimizes the negative influence of the conductive bar 5 on the permanent magnet magnetic circuit, and the magnetic lines can more easily enter the stator.

[0041] The permanent magnets are arranged in an embedded manner, and are separated from the air gap only by a magnetic bridge. The magnetic lines can more easily enter the stator and return to the rotor to form a loop. The permanent magnet steels arranged in a V shape have openings facing outward.

[0042] In the embodiment, the stator 2 has a cylindrical overall structure, is uniformly and equidistantly slotted on the inner side in the circumferential direction, and has a pitch angle of 30°. Double-layer fractional-slot concentrated windings are arranged in the slots, i.e., two element edges are arranged in each slot. The element edges of adjacent two slots are closed to form coils wound on the stator teeth in the middle. Compared with single-layer windings, the double-layer windings can double the number of coils, and the fractional-slot concentrated windings minimize the coil end portions. Specifically, there are 12 coil groups, and each phase has 4 coil groups.

[0043] The stator windings adopt concentrated windings, the conductors of adjacent two slots are closed to form coils wound on the stator teeth 1 in the middle, the coil end portions are short, copper is saved, copper loss is small, efficiency and power density can be improved, and cost can be saved.

[0044] The stator adopts fractional-slot windings, and the number of slots per pole per phase is a true fraction less than 1. Compared with an integer-slot motor, when the number of poles and the number of phases are the same, the number of stator slots is smaller. 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 an integer-slot motor, when the number of poles and the number of phases are the same, the number of stator slots is smaller.

[0045] The fractional-slot concentrated windings and the double-cage structure are applied to the asynchronous starting permanent magnet synchronous motor in the embodiment, which not only ensures that the stator windings are fractional-slot concentrated windings, but also belongs to the asynchronous starting permanent magnet synchronous motor. The winding loss is reduced, the motor efficiency is improved, energy saving is responded, a frequency converter is not needed, self-starting can be realized, material cost is saved, and system cost is reduced.

[0046] Embodiment Two

[0047] The embodiment provides a variable-pole switching method of a fractional-slot concentrated winding double-cage permanent magnet motor, which comprises the following steps.

[0048] The stator winding is directly connected to a power frequency three-phase alternating current power supply, the stator generates a rotating magnetic field, an induced current is generated in the rotor squirrel cage winding, and then a rotor rotating magnetic field is generated, the stator and rotor magnetic fields interact to generate an asynchronous torque to accelerate the rotor, when the rotor accelerates to a synchronous speed, winding switching is performed, after the switching, no large induced current is generated in the rotor winding, at this time, only the magnetic field generated by the permanent magnet is present on the rotor, and the asynchronous starting of the permanent magnet synchronous motor is realized.

[0049] During the motor starting process, when the rotor speed reaches the synchronous speed corresponding to the second polarity for the first time, winding switching is performed, all the coils in the stator slot are utilized before and after the switching, and only the connection mode between the coils is changed. Figures 8-9 As shown in the figure, the winding before the switching is a three-phase 12-slot 4-pole winding, the unit motor number of which is 2, and the winding arrangement is cyclic every 6 slots. Figures 6-7 As shown in the figure, the winding after the switching is a three-phase 12-slot 8-pole winding, the unit motor number of which is 4, and the winding arrangement is cyclic every 3 slots. Figure 6 、 8 As shown in the figure, the 12 coils of the 12-slot 4-pole winding are connected in reverse and the phase sequence of two phases is exchanged at will to obtain a 12-slot 8-pole winding, the specific harmonic magnetic motive force generated by the 12-slot 8-pole winding can be suppressed by the double squirrel cage structure, and no large induced current is generated in the rotor bar, so that the motor has good synchronous running capability.

[0050] During the motor starting process, the connection of the stator winding is switched, the magnetic motive force generated by the stator winding before and after the switching is different, the magnetic motive force generated by the stator winding before the switching enables the motor to have strong starting capability, and at the same time, a large current is induced in the rotor bar; the stator winding after the switching enables the motor to work in a synchronous state, and no large induced current is generated in the rotor bar.

[0051] Although the specific embodiments of the present application are described above in combination with the drawings, the description is not a limitation on the scope of protection of the present application, and those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the scope of protection of the present application.

Claims

1. A double-squirrel-cage permanent magnet motor with fractional slot concentrated windings, characterized in that, A method for switching a fractional-slot concentrated winding dual-squirrel-cage permanent magnet motor includes the following steps: during motor startup, when the rotor speed reaches synchronous speed for the first time, the winding is switched. 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 one and two phases are arbitrarily swapped to obtain the 12-slot 8-pole winding. The motor includes a stator and a rotor. The stator includes a stator winding design and a winding switching method. The stator adopts a three-phase fractional-slot concentrated winding, with two element sides placed in each slot. The element sides of two adjacent slots close to form a coil wound on the middle stator tooth. The rotor includes the rotor bar connection method and the relative number and positional relationship between the permanent magnets and the bars. Two sets of bars are provided on the outer circumference of the rotor. The two sets of bars are respectively connected to different end rings to form two independent squirrel cage structures. Each bar corresponds to the permanent magnet poles distributed in the circumferential direction of the rotor. Multiple bars are divided into two groups every other bar and are equally spaced on the outer side of the rotor.

2. The double squirrel-cage permanent magnet motor with fractional slot concentrated winding as described in claim 1, characterized in that, The guide bars in different groups are adjacent and equally spaced on the outside of the rotor.

3. A double-squirrel-cage permanent magnet motor with fractional slot concentrated windings as described in claim 1, characterized in that, The rotor has multiple permanent magnets evenly distributed along its circumference, and the permanent magnets are arranged in a V-shape.

4. A double squirrel-cage permanent magnet motor with fractional slot concentrated windings as described in claim 3, characterized in that, Each V-shaped arrangement of permanent magnets corresponds to one conductor bar.

5. A double-squirrel-cage permanent magnet motor with fractional slot concentrated windings as described in claim 3, characterized in that, The permanent magnets are internally distributed and separated from the air gap only by magnetic bridges.

6. A double-squirrel-cage permanent magnet motor with fractional slot concentrated windings as described in claim 1, characterized in that, Each guide bar on the rotor end face is located between two adjacent V-shaped permanent magnets.

7. A double-squirrel-cage permanent magnet motor with fractional slot concentrated windings as described in claim 1, characterized in that, The permanent magnets arranged in a V-shape have their included angle (V) facing one side of the rotor. Alternatively, each set of guide bars is connected by two end rings to form a cage structure. The two end rings that make up the same cage differ only in the axial length of one guide bar. The end rings that make up different cages are deflected relative to each other by a certain angle around the axis.

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