Stator structure of axial magnetic flux motor

Abstract

The utility model discloses a stator structure of an axial magnetic flux motor, which comprises a stator yoke, a plurality of stator teeth arranged at one end of the stator yoke in the circumferential direction and a cascade winding wound on the stator teeth, and every two stator teeth adjacent in the circumferential direction are mutually spaced to form a stator groove. The stator teeth comprise a plurality of stator sub-teeth arranged in the radial direction, every two adjacent stator sub-teeth in the radial direction are mutually spaced to form a stator slot belt, and winding coils wound outside all the stator sub-teeth on the radial outer side of the stator slot belt pass through the interior of each stator slot belt. The winding coil passing through the radial inner side stator slot belt is wrapped outside the winding coil passing through the radial outer side stator slot belt; and the wire diameters of the winding coils are equal. According to the utility model, the torque output capability of the motor can be improved, and compared with the mode of independently winding the inner and outer teeth of the stator to form the coil, the size of the stator slot belt can be reduced, and the copper consumption at the end part of the stator coil is reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to motor technical field especially relates to a kind of axial flux motor stator structure. BACKGROUND

[0002] Axial flux motor is also called disc type motor, its feature is that motor magnetic circuit passes through air gap along the axial direction of motor.Compared with radial flux motor, axial flux motor has higher power density, torque density and efficiency.

[0003] At present, to further improve power density and torque density, the improvement mode of axial flux motor mainly concentrates in assembly processing technology and motor heat dissipation technology.For example, the patent with application number 201910173110.0 adopts the mode of optimizing winding structure, improves motor power by improving motor slot fill factor, optimizing air gap flatness and improving motor inner diameter utilization rate.The patents with application numbers 202310432117.6 and 202010835768.6 all adopt the form of optimizing motor heat dissipation material or heat dissipation mode, improve motor electric load by increasing the maximum line current density allowed by motor, to realize the improvement of motor power density.

[0004] The air gap surface of axial flux motor for electromagnetic energy conversion is circular ring shape.The stator core is slotted to place winding coil, and the slotting divides the above-mentioned circular ring into multiple sector ring surfaces, so the stator tooth is sector ring shape, the circumferential length of tooth outside is greater than that of tooth inside, and the edge leakage of annular stator winding makes the edge of sector stator tooth easy to saturate, thereby leading to uneven distribution of magnetic flux density of sector stator core whole pole surface, therefore, the patent with application number CN202180027009.X cuts each sector stator tooth into multiple stator partial teeth, increases the coil quantity of tooth outside by winding coil on stator partial tooth from outside to inside in turn, and makes coil distribute multiple layers from inside to outside, instead of arranging along outer periphery, which improves electric load relative to stator of same size.However, the patent only proposes a scheme to improve electric load, does not consider how to maximize and optimize magnetic flux density through matching design of stator and winding, and does not consider how to realize high torque output in simple operation mode, with the increasing demand of market for operation sensitivity, miniaturization design and high torque of motor, how to maximize stator tooth to maximize magnetic flux density, and how to ensure higher output torque while improving operation performance, have gradually become problems to be solved urgently. UTILITY MODEL CONTENTS

[0005] In order to solve the technical problem that the existing axial flux motor cannot realize high torque output in simple operation mode, the utility model provides an axial flux motor stator structure to solve the above-mentioned problem.

[0006] The utility model discloses a technical scheme that solves its technical problem is: a kind of axial flux motor stator structure, including stator yoke, the circumferential direction arrangement of several stator teeth in one end of stator yoke and the cascade winding wound on stator tooth, two stator teeth that circumferential adjacent mutually interval form stator slot.

[0007] The stator tooth includes a plurality of stator teeth arranged along the radial direction, and the radially adjacent two stator teeth are spaced apart to form a stator slot belt. Each stator slot belt has a winding coil wound on the radially outer side of all stator teeth. The winding coil passing through the radially inner stator slot belt is wrapped outside the winding coil passing through the radially outer stator slot belt. The wire diameter of each winding coil is equal.

[0008] In an optional embodiment of the utility model, the stator slot belt is arc-shaped, and the slot width of any stator slot belt is less than the radial width of the stator tooth where it is located. l r .

[0009] In an optional embodiment of the utility model, the stator teeth and the stator teeth on the same diameter are arranged in a circumferential array, and the stator slot belts on the same diameter are connected to form a circular ring.

[0010] In an optional embodiment of the utility model, the stator slot between the two adjacent stator teeth is composed of a stator slot between each circumferentially adjacent two stator teeth. The circumferential width of the radially inner stator slot is less than the circumferential width of the radially outer stator slot.

[0011] In an optional embodiment of the utility model, each stator tooth includes a tooth body. The arc angle of any stator tooth is greater than the arc angle of the stator tooth radially outside the stator tooth, so that the tooth side surface extension line of the two radially adjacent stator teeth has a face distance difference.

[0012] In an optional embodiment of the utility model, the face distance difference between the tooth side surface of the kth stator tooth and the tooth side surface of the nth stator tooth in the same stator tooth from outside to inside is the single-side tooth body reduction width of the kth stator tooth. w k Then , wherein l i is the width of the ith stator slot belt from outside to inside, n is the total number of stator teeth in the same stator tooth, 1≤i≤n, 1≤k≤n.

[0013] In an optional embodiment of the utility model, the stator yoke gradually thickens as the radius increases.

[0014] ​In the optional embodiment of the utility model, the cross section of the stator yoke along the axial direction is trapezoidal.

[0015] In the optional embodiment of the utility model, the inner surface of the innermost stator tooth is flush with the inner surface of the stator yoke, and the outer surface of the outermost stator tooth is flush with the outer surface of the stator yoke.

[0016] In the optional embodiment of the utility model, the number of the winding coils is equal to the number of the stator teeth in the stator tooth, and the winding coils wound on the same stator tooth are connected in series to form a cascade winding.

[0017] The utility model discloses the beneficial effects are:

[0018] (1) the utility model discloses a segmented design of stator core by increasing the structure of stator slot belt, and at least two sets of winding coils adopt the inside and outside nesting mode, thereby improving the torque output capacity of motor and improving the control performance of motor.

[0019] (2) the utility model discloses that the tooth width of the stator tooth located on the outside is reduced to a certain extent, and the reduced tooth does not affect the motor performance since the stator tooth located on the outside is not saturated, and the unnecessary quality of motor can be reduced.

[0020] (3) the utility model discloses that when the axial flux motor is relatively large, the motor stator can be designed in multiple sections by adopting the form of multiple stator slot belts. l i and single-side tooth width reduction w k The magnetic field generated by the motor armature winding is more uniform, and the magnetic density is maximized.

[0021] (4) the utility model discloses that the stator yoke is optimized from the traditional uniform design of equal thickness to the non-uniform design of increasing thickness with the increase of stator radius, the magnetic resistance is reduced by increasing the magnetic conduction area in the high magnetic flux area, the loss in the area is reduced, thereby improving the output torque of motor and realizing the improvement of motor torque density. BRIEF DESCRIPTION OF DRAWINGS

[0022] The utility model will be further described below in combination with the drawings and examples.

[0023] Figure 1It is the three-dimensional view of the embodiment of the axial flux motor stator structure of the utility model;

[0024] Figure 2 It is the axial sectional view of the embodiment of the axial flux motor stator structure of the utility model;

[0025] Figure 3 It is the explosion view of the embodiment of the axial flux motor stator structure of the utility model;

[0026] Figure 4 It is the three-dimensional view of the stator core in the embodiment of the utility model;

[0027] Figure 5 It is the arrangement schematic view of the plurality of cascade windings in the embodiment of the utility model;

[0028] Figure 6 It is the connection mode schematic view of the winding coil in the cascade winding of the utility model;

[0029] Figure 7 It is the partial enlarged view of the stator core in the embodiment of the utility model;

[0030] Figure 8 It is the connection schematic view of the stator tooth and the cascade winding in the embodiment of the utility model;

[0031] Figure 9 It is the half sectional schematic view of the axial flux motor stator structure of the utility model;

[0032] Figure 10 It is the size schematic view of the single-side tooth body width reduction in the utility model;

[0033] Figure 11 It is the winding mode schematic view of the winding coil in the utility model;

[0034] Figure 12 It is the winding mode schematic view of the winding coil in the traditional mode.

[0035] In the drawing, 1, stator core, 11, stator tooth, 111, first stator tooth, 112, second stator tooth, 113, third stator tooth, 11i, i-th stator tooth, 11n, n-th stator tooth, 12, stator yoke, 13, stator slot, 131, first stator sub-slot, 132, second stator sub-slot, 133, third stator sub-slot, 14, stator slot belt, 141, first stator slot belt, 142, second stator slot belt, 14i, i-th stator slot belt, 2, cascade winding, 21, first layer winding coil, 22, second layer winding coil, 2i, i-th layer winding coil, 2n, n-th layer winding coil, 3, end head, 4, tooth body. Detailed Implementation

[0036] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0037] Example 1

[0038] like Figures 1-4 As shown, an axial flux motor stator structure includes a stator core 1 and cascaded windings 2. The stator core 1 includes a stator yoke 12 and a plurality of stator teeth 11 arranged circumferentially at one end of the stator yoke 12. Two circumferentially adjacent stator teeth 11 are spaced apart to form stator slots 13. The number of cascaded windings 2 is equal to the number of stator teeth 11.

[0039] The stator teeth 11 include multiple stator teeth arranged radially. Two radially adjacent stator teeth are spaced apart to form stator slot strips 14. Each stator slot strip 14 contains a winding coil wound around all the stator teeth on its radially outer side. The winding coils passing through the radially inner stator slot strip 14 are wrapped around the winding coils passing through the radially outer stator slot strip 14. That is, the first layer of winding coils 21 is wound around the outermost stator teeth and passes through the outermost stator slot strip 14. The second layer of winding coils 22 is located outside the first layer of winding coils 21. The second layer of winding coils 22 is wound around the two outermost stator teeth and passes through the next outermost stator slot strip 14. The wire diameter of each winding coil is equal. Different wire diameters of winding coils result in different space occupation and different resistances. For the sake of standardized design, this invention sets the wire diameter of each winding coil to be equal.

[0040] This invention divides the traditional integral stator teeth 11 into independent stator sub-teeth, thereby forming stator slot strips 14 between adjacent stator sub-teeth for winding coils. This reduces the maximum distance between various parts of the stator teeth 11 and the coils, improving magnetic saturation. Consequently, it can increase the electrical load of the motor with the same size stator core 1. Furthermore, the winding coils employ an inner and outer nested winding method, such as... Figure 11 The diagram shows a nested winding method, with coils wound around the outside of each stator tooth (e.g., ...). Figure 12 Compared to (as shown), this design can reduce the width of the stator slot strip 14 and also reduce the amount of copper used at the ends of the coil windings. Connecting the inner and outer windings in series sequentially can increase the motor's output torque.

[0041] Regarding the design of stator slot 14:

[0042] The stator slot belt 14 is used to separate two radially adjacent stator teeth, and the winding is wound, so the stator slot belt 14 is located inside the stator tooth 11, and the slot width of any stator slot belt 14 is less than the radial width of the stator tooth 11 l The stator slot belt 14 is used to separate two radially adjacent stator teeth, and the winding is wound, so the stator slot belt 14 is located inside the stator tooth 11, and the slot width of any stator slot belt 14 is less than the radial width of the stator tooth 11 r The shape of the stator slot belt 14 is determined by the inner and outer radial surfaces of the stator tooth, and the stator slot belt 14 can be any shape, for easy processing, and also to improve the uniformity of the magnetic flux distribution on the stator tooth, the stator slot belt 14 is preferably a circular arc shape, at this time, each stator tooth on the stator tooth 11 is a circular arc structure with the same center and different radii.

[0043] The distribution of the stator tooth 11 and the spacing between the stator teeth on each stator tooth 11 can be set according to actual needs, for example, the number of turns of the winding is set according to different parts, in the conventional setting, the stator tooth 11 and the stator tooth on the same diameter are arranged in an array along the circumference, and the stator slot belt 14 located on the same diameter is connected to form a circular ring shape, so that the winding coil structure, electrical load and magnetic flux distribution of each stator tooth 11 are the same, and the symmetry of the stator structure and the magnetic flux is realized. In addition, the stator slot belt 14 is located only inside the stator tooth 11, that is, the stator slot belt 14 is not arranged on the inner and outer sides of the stator tooth 11, that is, the inner surface of the innermost stator tooth is flush with the inner surface of the stator yoke 12, and the outer surface of the outermost stator tooth is flush with the outer surface of the stator yoke 12, thereby reducing.

[0044] Regarding the winding method of the winding coil:

[0045] In the preferred embodiment of the utility model, the plurality of winding coils wound on the same stator tooth are connected in series, and the current of each winding coil is the same in the series connection state, so that a plurality of controllers are not required to control the winding coils, the rapid control of the current can be realized, and the control performance of the motor is improved. If the traditional integral stator tooth 11 structure is used for winding series connection, the effect of improving the output torque of the motor cannot be achieved, and the utility model forms a complete cascade winding 2 by connecting a plurality of winding coils in series under the premise of the structure of the plurality of slot belts and the plurality of windings, which not only improves the output torque of the motor, but also improves the control performance of the motor. The number of winding coils is equal to the number of stator teeth in the stator tooth 11, the i th winding coil 2i is formed by winding the i th stator slot belt 14i and all the stator teeth outside it from outside to inside, the i th winding coil 2i is surrounded by the i-1 th winding coil, and the two winding coils are connected in series, wherein i is a positive integer.

[0046] Assuming the total number of stator teeth is n, the stator teeth are named from outside to inside as the first stator tooth 111, the second stator tooth 112, …, the i-th stator tooth, …, the n-th stator tooth 11n. Correspondingly, the stator slot band 14 between the first stator tooth 111 and the second stator tooth 112 is the first stator slot band 141. The first layer of winding coils 21 passes through the first stator slot band 141 and is wound outside the first stator tooth 111. The second layer of winding coils 22 is wrapped outside the first layer of winding coils 21, and only passes through the second stator slot band 142 and is wound outside the first stator tooth 111 and the second stator tooth 112. Similarly, the i-th layer of winding coils 2i only passes through the i-th stator slot band 14i and is wound outside the first stator tooth 111 to the i-th stator tooth 11i. The cascaded winding 2 after winding is shown in Figure 6 As the winding coils of adjacent layers are connected in series, the cascaded winding 2 has only two ends 3, which are located at the ends of the first layer of winding coils 21 and the n-th layer of winding coils 2n, respectively.

[0047] Figure 7 And Figure 8 The structure of the stator core 1 in the axial flux motor stator structure described in this embodiment is shown in the figure. Each stator tooth 11 has three stator teeth from outside to inside, namely the first stator tooth 111, the second stator tooth 112, and the third stator tooth 113. The stator tooth 11 has two stator slot bands 14, and the winding coils are wound in three layers.

[0048] Stator slot 13:

[0049] The stator slot 13 between the two adjacent stator teeth 11 is composed of the stator slot between each circumferentially adjacent two stator teeth. The stator slot on both sides of the first stator tooth 111 is the first stator slot 131, the stator slot on both sides of the second stator tooth 112 is the second stator slot 132, and so on until the n-th stator slot. For the case of three stator teeth in this embodiment, the stator slot 13 is composed of three stator slots, which are the first stator slot 131, the second stator slot 132, and the third stator slot 133 (as shown in Figure 7 ).

[0050] Because the diameter of the inner stator slot is smaller and the diameter of the outer stator slot is larger, considering the symmetry of the structure, the circumferential width of the stator slot located on the radial inner side is smaller than that of the stator slot located on the radial outer side.

[0051] Embodiment two

[0052] In traditional structures, the arc angles of stator teeth 11 are the same on different diameters. When divided into multiple stator teeth, the conventional approach is to set the arc angle of each stator tooth to be the same. However, as described in the background art, since the circumference length of the outer side of the stator tooth 11 is greater than the circumference length of the inner side, the part of the stator tooth 11 closer to the radial outer side is usually less saturated. Although segmenting the stator teeth can alleviate this unsaturation phenomenon to some extent, the number of stator teeth segments is limited, and there will still be some uneven distribution. Therefore, the problem of unsaturation on the outer side of the stator teeth 11 cannot be completely solved by segmenting the stator teeth. This embodiment limits the size of the stator teeth based on Embodiment 1, reducing the circumferential width of the outer stator teeth. Specifically, each stator tooth includes a tooth body 4, and the arc angle of any stator tooth is greater than the arc angle of the stator tooth located radially outer of that stator tooth, thus creating a surface distance difference between the extended lines of the tooth body 4 of two radially adjacent stator teeth. Figure 7 Taking the case of three stator teeth as an example, the arc angle of the first stator tooth 111 is greater than that of the second stator tooth 112, and the arc angle of the second stator tooth 112 is greater than that of the third stator tooth 113.

[0053] Since each stator tooth 11 shares the same axis of symmetry, the arc angle of the stator tooth determines the extent of the extended lines encompassing the sides of the tooth body 4. When the arc angle of the inner stator tooth is greater than that of the outer stator tooth, the extended lines of the sides of the tooth body 4 of the outer stator tooth are contained within the extended lines of the sides of the tooth body 4 of the inner stator tooth. By reducing the circumferential width of the outer stator teeth, the problems of low utilization and unsaturation on the outer side of the stator teeth 11 can be fundamentally solved, reducing the weight of the motor while ensuring magnetic flux.

[0054] By reasonably setting the circumferential width reduction of the stator teeth, the utilization rate of stator teeth 11 can be maximized. The reduction amount of stator teeth needs to be matched with the winding form of the winding coil. In the cascaded winding 2 structure adopted in this utility model, the surface distance difference between the side surface of the tooth body 4 of the kth stator tooth from the outside to the inside and the side surface of the tooth body 4 of the nth stator tooth 11 is equal to the reduction width of the single side tooth body 4 of the kth stator tooth. w k ,but At that time, the saturation of stator teeth 11 can be maximized, among which, l i Let be the width of the i-th stator slot 14 counted from the outside in, and n be the total number of stator teeth in the same stator tooth 11, 1≤i≤n, 1≤k≤n.

[0055] byFigure 10 For example, in the case of three stator teeth in the stator tooth 111, the tooth body 4 of the first stator tooth 111 is located inside the tooth body 4 of the second stator tooth 112, and the tooth body 4 of the second stator tooth 112 is located inside the tooth body 4 of the third stator tooth 113. The difference between the side surface extension line of the tooth body 4 of the first stator tooth 111 and the side surface extension line of the tooth body 4 of the third stator tooth 113 is the single-side tooth body 4 reduction width of the first stator tooth 111 The difference between the side surface extension line of the tooth body 4 of the second stator tooth 112 and the side surface extension line of the tooth body 4 of the third stator tooth 113 is the single-side tooth body 4 reduction width of the second stator tooth 112 w 2 = l 2 .

[0056] Embodiment three

[0057] In the above embodiment, only the uniformity of the magnetic flux density distribution on the stator tooth 11 is solved, and the load capacity of the stator yoke 12 is not considered. In theory, for the sector-shaped permanent magnet steel of the axial flux motor, the magnetic flux of the outer side is larger than that of the inner side when the magnetic flux density is the same, and the difference between the magnetic flux of the inner side and the outer side is not obvious under the traditional coil winding mode. Therefore, the use of the equal-thickness stator yoke 12 structure will not cause a large magnetic flux loss. Due to the multi-layer setting of the winding coil, the coil quantity of the outer side of the stator yoke 12 is more than that of the inner side of the stator yoke 12. If the radial equal-thickness stator yoke 12 is still used, when the inner side of the stator yoke 12 is just saturated, the magnetic flux of the outer side of the stator yoke 12 is large, which will cause the over-saturation of the part and the sharp increase of the loss. Therefore, on the basis of the above embodiment, the radial equal-thickness structure of the stator yoke 12 is changed to gradually thicken with the increase of the radius. In the preferred embodiment, as shown in the figure, the axial cross section of the stator yoke 12 is trapezoidal. At this time, the stator yoke 12 can not only improve the radial magnetic flux non-uniformity and the stator yoke 12 problem, but also ensure the structural symmetry, be easy to process, and increase the heat dissipation area and improve the service life of the motor through the thickening design of the stator yoke 12. Figure 9

[0058] In the description of the utility model, it is understood that the orientation or position relationship indicated by the terms "center", "length", "width", "thickness", "left", "right", "inner", "outer", "axial", "radial", "circumferential" and the like is the orientation or position relationship based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the utility model and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the utility model.

[0059] ​In addition, the terms "first", "second" and the like are used only for descriptive purposes and do not denote or imply relative importance. In the description of the present application, it should be explained that, unless otherwise explicitly specified and limited, the terms "connected" and "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. In addition, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0060] In the present specification, the illustrative description of the terms does not necessarily refer to the same embodiment. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments in a suitable manner.

[0061] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A stator structure for an axial flux motor, characterized in that: It includes a stator yoke (12), a number of stator teeth (11) arranged in a circumferential direction at one end of the stator yoke (12), and a cascaded winding (2) wound on the stator teeth (11). Two circumferentially adjacent stator teeth (11) are spaced apart to form stator slots (13). The stator teeth (11) include a plurality of stator teeth arranged radially. Two adjacent stator teeth are spaced apart to form stator slots (14). Each stator slot (14) contains a winding coil wound around all the stator teeth on its radial outer side. The winding coils that pass through the inner stator slot (14) are wrapped around the outer stator slot (14). The wire diameter of each winding coil is the same.

2. The axial flux motor stator structure according to claim 1, characterized in that: The stator slot (14) is arc-shaped, and the slot width of any stator slot (14) is... l Smaller than the radial width of the stator tooth (11) it is located r .

3. The axial flux motor stator structure according to claim 1, characterized in that: The stator teeth (11) and the stator sub-teeth on the same diameter are arranged in a circumferential array, and the stator slots (14) on the same diameter are connected to form a ring.

4. The axial flux motor stator structure according to claim 1, characterized in that: The stator slot (13) between two adjacent stator teeth (11) is composed of stator slots located between two adjacent stator teeth in each circumferential direction, and the circumferential width of the stator slot located on the radially inner side is smaller than the circumferential width of the stator slot located on the radially outer side.

5. The axial flux motor stator structure according to claim 4, characterized in that: Each of the stator teeth includes a tooth body (4), and the arc angle of any stator tooth is greater than the arc angle of the stator tooth located radially outside the stator tooth, so that there is a surface distance difference between the side extension lines of the tooth bodies (4) of two radially adjacent stator teeth.

6. The axial flux motor stator structure according to claim 5, characterized in that: Let the difference in surface distance between the side of the tooth body (4) of the kth stator tooth (11) from the outside to the inside and the side of the tooth body (4) of the nth stator tooth be the width of the single side of the tooth body (4) of the kth stator tooth. w k ,but ,in, l i Let be the width of the i-th stator slot (14) counted from the outside in, and n be the total number of stator teeth in the same stator tooth (11), 1≤i≤n, 1≤k≤n.

7. The axial flux motor stator structure according to claim 5, characterized in that: The stator yoke (12) gradually thickens as the radius increases.

8. The axial flux motor stator structure according to claim 7, characterized in that: The cross section of the stator yoke (12) along the axial direction is trapezoidal.

9. The axial flux motor stator structure according to claim 2, characterized in that: The innermost stator tooth inner surface is flush with the inner surface of the stator yoke (12), and the outermost stator tooth outer surface is flush with the outer surface of the stator yoke (12).

10. The axial flux motor stator structure according to claim 1, characterized in that: The number of winding coils is equal to the number of stator teeth in the stator teeth (11), and several winding coils wound on the same stator teeth (11) are connected in series to form a cascaded winding (2).

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