Motor stator and permanent magnet motor with stepped winding and stepped slots with protective layer

Abstract

The present invention provides a motor stator and permanent magnet motor with a stepped winding and stepped slots with a protective layer, belonging to the field of motor technology. Each phase of the stepped stator winding includes N layers of coils radially distributed in the stator slots, and each phase winding includes at least N / 2 parallel branches. The current flowing through each parallel branch is different, but the current density in the conductors of each parallel branch is the same. All parallel branches are ultimately connected in parallel to form a phase winding, which includes at least one layer of stator winding with a protective layer starting from the conductor closest to the air gap, where N is an even number greater than or equal to 2. The present invention reduces the eddy current loss of the conductor close to the air gap; reduces the copper loss and temperature rise of the conductor close to the air gap, solves the problem of uneven temperature distribution of the conductor in the stator slot, and improves the operating reliability and thermal stability of the motor; on the basis of having a high slot fill rate, it improves the iron core utilization rate. Under the same power motor, the application of stepped windings in stepped slots or trapezoidal slots reduces the stator core diameter.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to a motor stator and a permanent magnet motor having stepped windings and stepped slots with protective layers, which can reduce coil temperature rise near an air gap and balance conductor temperature distribution in stator slots. Background Art

[0002] The rectangular slots and rectangular conductor windings currently used in motors have attracted considerable attention due to their high slot fill factor, high power density, and excellent conductor thermal conductivity. However, due to the large cross-sectional area of ​​rectangular conductors and the high transverse leakage flux near the air gap in the stator slots, the conductors in the area near the air gap experience high eddy current losses due to the transverse leakage flux, leading to a higher temperature rise. Furthermore, the conductors in the stator slots near the air gap are not well-suited for heat dissipation. Consequently, the copper loss caused by the armature current and the eddy current losses caused by the transverse leakage flux combine to increase the conductor temperature in this area, which can, in severe cases, accelerate the aging of the conductor insulation. Furthermore, the uneven temperature distribution within the stator slots generates thermal stress, which can also lead to stator failure. The high temperature in the conductors near the air gap is transferred through the air gap to the rotor permanent magnets, increasing their temperature, reducing their performance and affecting motor efficiency. In severe cases, this can lead to permanent magnet demagnetization, which can cause serious motor failure. These factors significantly impact the operating efficiency, reliability, and life of motors with rectangular conductor windings. Summary of the Invention

[0003] The object of the present invention is to provide a motor stator and a permanent magnet motor with a stepped winding and stepped slots with a protective layer, which reduces the electrical loss and eddy current loss of the conductor near the air gap side and thus reduces the temperature rise of the conductor, thereby improving the life, reliability and efficiency of the motor, so as to solve at least one technical problem existing in the above-mentioned background technology.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] On the one hand, the present invention provides a motor stator provided with a stepped winding with a protective layer and a stepped slot. Each phase winding of the stepped stator winding includes N layers of coils distributed radially in the stator slots, and each phase winding includes at least N / 2 parallel branches. The current flowing through each parallel branch is different, but the current density in the conductors of each parallel branch is the same to ensure the utilization rate of the copper conductor; all parallel branches are ultimately connected in parallel to form a phase winding, starting from the conductor closest to the air gap, and including at least one layer of stator winding with a protective layer, where N is an even number greater than or equal to 2.

[0006] Preferably, if the motor stator is in a double-layer winding form, the cross-sectional areas of the coil conductors of two adjacent layers are the same; if the motor stator is in a single-layer winding form, it contains at least two layers of coil conductors with different cross-sectional areas, and the adjacent two layers or one layer with the same cross-sectional area constitute a winding branch, or the above two types of mixed windings can be used, and finally all branches are connected in parallel to form a phase winding.

[0007] Preferably, the conductors in the stator slots have different current-carrying cross-sectional areas, and the winding branches composed of conductors with different current-carrying cross-sectional areas are finally connected in parallel. AX , then the voltage at each branch end is the same as U AX , and the conductor cross-sectional area is different, according to R k =ρl / S k It can be seen that the conductor resistance is different, and the total resistance of the branch with a large conductor cross-sectional area is small, and vice versa. According to I k =U AX / R k The current can be automatically distributed unevenly to the branches with different conductor cross-sectional areas in the stator slots. k =J k ×S k It can be seen that the current density J k Under the same conditions, the smaller the conductor cross-sectional area, the smaller the current, and vice versa, the larger the current, and according to It can be seen that the smaller the conductor cross-sectional area, the smaller the conductor copper loss, and thus the smaller the heat generated by the conductor copper loss; for the inner rotor motor, using the stepped stator winding, the current-carrying cross-sectional area of ​​the conductor close to the air gap is smaller than the current-carrying cross-sectional area of ​​the conductor close to the stator yoke. Therefore, the closer the conductor is to the stator yoke, the greater the heat generated by the copper loss, and vice versa. That is, a larger current is distributed to the conductor close to the stator yoke with a larger cross-sectional area and conducive to heat dissipation, and a smaller current is distributed to the conductor close to the air gap with a smaller cross-sectional area and not conducive to heat dissipation. Therefore, the stepped stator winding can effectively solve the problems of excessive temperature rise of the conductor close to the air gap and uneven temperature rise of the inner and outer windings, while improving the core utilization rate and slot fill rate. According to formula I k =U AX / R k , R k =ρl / S k , It can be seen that the relationship between the copper loss of the i-th layer winding and the k-th layer is P Cui =S i / S k P Cuk .

[0008] Where: U AX is the phase voltage of phase A, J k is the current density of the k-th layer winding, I k is the kth layer winding current, Rk is the total resistance of the k-th layer winding converted to the reference operating temperature, ρ is the resistivity of the copper conductor, l is the effective conductor length in the stator slot, S k Cross-sectional area of ​​the kth layer conductor, P Cu is the total copper loss of each phase winding, P Cui is the copper loss of the i-th layer winding, P Cuk is the copper loss of the k-th layer winding.

[0009] Preferably, two adjacent layers or one layer with the same cross-sectional area form a winding branch, and finally all the branches are connected in parallel to form a phase winding, so that the induced electromotive force between all branches is the same. The induced electromotive force between all branches is the same to avoid the generation of circulating current between different branches due to the imbalance of induced electromotive force, thereby causing additional loss. According to E φ1 =4.44fNk w1 φ1 shows that if the total number of coil turns N and winding factor k in series between different branches w1 The product of is the same, then the induced electromotive force between different branches is the same.

[0010] Where: E φ1 is the fundamental electromotive force of each phase winding, f is the power supply frequency, and φ1 is the main pole flux.

[0011] Preferably, the widths of adjacent conductors with different cross-sectional areas should satisfy

[0012] Where l′ represents the width of the wide conductor, l represents the width of the narrow conductor, h represents the height of the narrow conductor, r represents the number of narrow conductor layers with the same cross-sectional area, d represents the insulation thickness between conductor layers in the stator slot, and Q represents the number of stator slots.

[0013] Total cross-sectional area of ​​all conductors in stator slots with stepped windings The total conductor cross-sectional area S = n × S1 is the same as that of an equivalent motor without a stepped winding (i.e., the stator slots are conductor windings with the same cross-sectional area), ensuring that the total current carrying capacity of each phase winding of the stepped winding is the same as that of the equivalent conventional motor.

[0014] Where: S' is the total cross-sectional area of ​​the conductor in the stepped winding slot, S k ′ is the cross-sectional area of ​​the kth conductor in the stepped winding slot, n is the total number of conductors in the slot, k represents the kth conductor, S is the total cross-sectional area of ​​the conductors in the winding slot with the same cross-sectional area of ​​the motor conductor, and S1 is the cross-sectional area of ​​the single-layer conductor of the winding with the same cross-sectional conductor.

[0015] Preferably, the protective layer is perpendicular to the transverse leakage flux direction and is arranged on both sides of the conductor in the slot. The formula for the distribution of magnetic field intensity and current density in the effective conductor of the coil in the stator slot caused by the transverse leakage flux of the stator slot is: It can be seen that the closer the stator slot is to the air gap, the greater the transverse leakage flux is, and therefore the eddy current loss of the conductor in this area is greater. Adding a protective layer of stainless steel material with weak magnetic permeability and electrical conductivity can reduce the total magnetic flux inside the conductor in the stator slot, thereby reducing the eddy current loss and temperature rise of the conductor in the stator slot.

[0016] Where: is the stator slot transverse leakage magnetic field intensity, b s is the average slot width where the conductor is located, b is the conductor width, μ0 is the vacuum magnetic permeability, σ is the electrical conductivity of the copper conductor, is the current density in the conductor.

[0017] Preferably, the thickness of the protective layer is greater than the skin depth when the transverse leakage flux frequency is f

[0018] Wherein, μ is the magnetic permeability of the protective layer material, and σ is the electrical conductivity of the protective layer material.

[0019] Preferably, a phenolic resin layer is disposed between the protective layer and the conductor, and both the protective layer and the phenolic resin layer are disposed only within the effective conductor segments within the stator slots. The protective layer is a stainless steel protective layer, and the phenolic resin layer is disposed between the stainless steel protective layer and the conductor to increase the rigidity of the stainless steel protective layer. Because the stainless steel layer is very thin and has poor rigidity, the stainless steel protective layer is fixed to the phenolic resin layer, which is then brought into contact with the conductor, and finally varnished and wrapped with an insulating layer. Both the stainless steel protective layer and the phenolic resin layer are disposed only within the effective conductor segments within the stator slots. The phenolic resin layer provides a thermal insulation effect, reducing the transfer of heat generated by eddy current losses in the stainless steel protective layer into the conductor, while effectively weakening vibrations of the winding conductor within the slots.

[0020] In a second aspect, the present invention provides a permanent magnet motor comprising the motor stator having the stepped winding with a protective layer and the stepped slots as described above.

[0021] Preferably, the stator slot is a stepped slot, the circumferential area of ​​the core near the stator yoke is larger, and a wide slot is set, the circumferential area of ​​the core near the air gap is smaller, and a narrow slot is set, and the width between adjacent slots meets By A t =K Fe l t b t It can be seen that if the tooth magnetic flux φ t , core stacking coefficient K Fe and core length l t unchanged, the tooth magnetic flux density B t Only with tooth width b t Therefore, if the tooth width is the same, it is beneficial to improve the utilization rate of the stator core. If the slot width is different and wider conductors are placed in the wider slot section, the slot fill rate will be improved.

[0022] Where: l k+1 is the width of the wider slot in the k+1th layer, l k is the width of the narrower slot in the kth layer, h k is the height of the narrow slot in the kth layer, Q is the number of stator slots, A t is the calculated cross-sectional area of ​​the tooth.

[0023] The beneficial effects of the present invention are as follows: the eddy current loss of the conductor close to the air gap is reduced, thereby achieving the effect of lowering the conductor temperature in this area; the copper loss of the conductor close to the air gap side is reduced, the temperature rise of the conductor in this area is reduced, the problem of uneven temperature distribution of the conductor in the stator slot is solved, and the operating reliability and thermal stability of the motor are improved; on the basis of a high slot fill rate, the iron core utilization rate is improved. Under the same power motor, the application of stepped windings in stepped slots or trapezoidal slots can reduce the stator core diameter to a certain extent.

[0024] Additional aspects and advantages of the present invention will be set forth in part in the following description, will be obvious from the following description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a schematic diagram of a stepped winding with a stainless steel protective layer when using trapezoidal slots according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a stepped winding with a stainless steel protective layer using rectangular slots according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of a stepped winding with a stainless steel protective layer when the stepped slots are described in an embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram of the winding structure with a stainless steel protective layer according to an embodiment of the present invention.

[0030] Figure 5 Schematic diagram of the distribution of transverse leakage flux in stator slots according to an embodiment of the present invention.

[0031] Figure 6 Expanded diagram of phase A winding of stepped winding when it is trapezoidal slot or stepped slot

[0032] Figure 7This is the equivalent circuit diagram of the A phase of the stepped winding when using the trapezoidal slot or stepped slot according to the embodiment of the present invention.

[0033] Figure 8 This is an expanded view of the A-phase winding of the rectangular slot stepped winding according to an embodiment of the present invention.

[0034] Figure 9 This is the equivalent circuit diagram of the stepped winding phase A in the rectangular slot according to an embodiment of the present invention.

[0035] Among them: 001-stator lamination; 002-trapezoidal stator slot; 003-main insulation; 004-conductor insulation; 005-stator tooth; 006-1st and 2nd layer winding conductors; 007-i-1st and i-th layer winding conductors; 008-kth and k+1th layer conductors with stainless steel and phenolic resin protective layers; 009-n-1st and nth layer conductors with stainless steel and phenolic resin protective layers; 010-phenolic resin protective layer; 011-conductive stainless steel protective layer; 101-rectangular stator slot; 102-rectangular conductors with the same cross-sectional area; 201-step slot. DETAILED DESCRIPTION

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

[0037] Those skilled in the art will understand that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0038] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0039] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a," "an," "said," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0040] In the description of this specification, reference to the terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless otherwise inconsistent.

[0041] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0042] In the description of this specification, the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing the present technology and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they should not be understood as limiting the present technology.

[0043] Unless otherwise specified or limited, the terms "installed," "connected," "connected," and "disposed" should be understood broadly. For example, they may refer to fixed connection or disposition, detachable connection or disposition, or integral connection or disposition. Those skilled in the art will understand the specific meanings of these terms in this technology based on specific circumstances.

[0044] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0045] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0046] Example 1

[0047] Rectangular conductor windings and rectangular slots have attracted considerable attention due to their advantages, including high slot fill factor, high power density, and high efficiency. However, due to the large cross-sectional area of ​​the conductor, eddy current losses are high due to transverse magnetic leakage. Furthermore, heat dissipation in the stator slots near the air gap is poor, and transverse magnetic leakage is greater near the air gap than near the stator yoke. These factors, combined, lead to uneven temperature distribution in the stator slots, with higher temperature rise near the air gap. This can reduce motor efficiency and reliability, and even cause serious motor failure.

[0048] To address the above problems, this embodiment 1 proposes a conductor winding with a stainless steel protective layer, a stepped winding, and a stepped slot to improve the utilization rate of the stator core, reduce the eddy current loss and copper loss of the conductor close to the air gap, and solve the problem of uneven radial temperature distribution of the conductor in the stator slot, thereby improving the reliability and efficiency of the motor.

[0049] The rectangular conductor with stainless steel protective layer, such as Figure 4 As shown, stainless steel protective layers 010 are placed on both sides of rectangular conductor 008. The protective layers are the same height as rectangular conductor 008. A phenolic resin layer is placed between rectangular conductor 008 and stainless steel protective layer 010 to increase the rigidity of the stainless steel layer, prevent heat transfer from the stainless steel layer to the conductor, and reduce conductor vibration. The stainless steel layer has weak magnetic permeability and electrical conductivity, effectively reducing eddy current losses in the conductor within the slot caused by transverse magnetic leakage flux.

[0050] The stainless steel protective layer can also be made of other materials with better electrical conductivity and magnetic permeability, such as copper-iron alloy or iron-nickel alloy, according to the skin depth formula It can be seen that when the motor is running at high speed, the magnetic field frequency is relatively large. If the material magnetic permeability μ and electrical conductivity δ are high, the eddy current penetration depth is small due to the skin effect. Therefore, adding a protective layer can concentrate the eddy current loss on the protective layer and reduce the eddy current loss of the copper conductor. Since the phenolic resin layer plays a heat insulating role, it can effectively reduce the temperature of the stainless steel protective layer and conduct it to the conductor in the slot, thereby reducing the temperature of the conductor close to the air gap.

[0051] In this embodiment 1, a stainless steel material with weak magnetic conductivity is selected, and it is assumed that the relative magnetic permeability μ r =75, conductivity σ = 9.9 × 10 6 S / m, the switching frequency of the power inverter is f = 4 kHz, then the skin depth of the transverse leakage flux acting on the protective layer can be calculated to be δ = 0.29 mm. Therefore, taking the thickness of the protective layer as 0.3 mm can effectively weaken the transverse leakage flux in the conductor, thereby reducing the eddy current loss in the conductor.

[0052] The thickness of the phenolic resin layer is determined according to the stator slot width, the conductor width required by the design, and the width of the stainless steel protective layer.

[0053] In this embodiment 1, the ladder winding, such as Figure 1-3 As shown, the stepped winding is characterized in that the stator slots contain conductors with different cross-sectional areas, forming a stepped arrangement.

[0054] If it is a trapezoidal groove or a stepped groove, such as Figure 2 and Figure 3 As shown, the stator teeth have equal tooth width and the core utilization rate is high. This is because wide conductors are arranged at positions with larger slot widths and narrow conductors are arranged at positions with smaller slot widths. However, the total current carrying capacity of all conductors in the slots should remain unchanged, that is, the reduced conductor cross-sectional area in the narrow conductor is equal to the increased cross-sectional area in the wide conductor.

[0055] If a rectangular slot is used, such as Figure 2 As shown, the stepped winding is arranged in the 1-3 conductor layers in the slot close to the air gap to reduce the conductor current carrying capacity and thus reduce the temperature rise of the conductor in this area caused by copper loss and eddy current loss.

[0056] The conductors in the stator slots have different widths but the same height, resulting in different conductor cross-sectional areas. The slot width near the air gap is smaller than the stator slot width near the stator yoke due to the smaller core circumference. Therefore, the current-carrying cross-sectional area of ​​the conductors in the stator slots near the air gap is smaller.

[0057] Conductors with different cross-sectional areas form different branches of the winding, and finally multiple branches are connected in parallel to form a phase winding, such as Figure 4 As shown. Since each phase winding terminal voltage U AX If the total current carrying capacity of the winding I remains unchanged, the branch currents formed by conductors with different cross-sectional areas will be different, such as Figure 5 As shown, and by formula I k =U AX / R k ,R k =ρl / S k It can be seen that the current of the k-th layer winding is I k =U AX S k / ρl, so if it is assumed that the total length l of the branch coil conductor is the same, the smaller the conductor cross-sectional area, the smaller the current flowing through it, that is: the larger current is distributed to the conductor with a larger cross-sectional area and close to the stator yoke, which is conducive to heat dissipation, and the smaller current is distributed to the conductor with a smaller cross-sectional area and close to the air gap, which is not conducive to heat dissipation.

[0058] Where: U AX is the phase voltage of phase A, I k is the kth layer winding current, R k is the total resistance of the k-th layer winding converted to the reference operating temperature, ρ is the resistivity of the copper conductor, l is the effective conductor length in the stator slot, S k is the cross-sectional area of ​​the conductor in the kth layer.

[0059] Therefore, the heat generated by the copper loss of the conductor near the air gap is small, because the total copper loss of the conductor near the air gap is And the relationship between the copper loss of the i-th layer winding and the k-th layer is P Cui =S i / S k P Cuk Therefore, the ladder winding can reduce the temperature rise of the conductor close to the air gap and solve the problem of uneven temperature rise of the conductor in the stator slot. k is the kth layer winding current, R k is the total resistance of the k-th layer winding converted to the reference operating temperature, S k Cross-sectional area of ​​the kth layer conductor, P Cu is the total copper loss of each phase winding, P Cui is the copper loss of the i-th layer winding, P Cuk is the copper loss of the k-th layer winding.

[0060] In this embodiment 1, the stepped groove, such as Figure 3 As shown, for the inner rotor motor, the circumferential area of ​​the core near the stator yoke is larger, and a wide slot is set. The circumferential area of ​​the core near the air gap is smaller, and a narrow slot is set. The width of adjacent step slots should meet the width between adjacent slots. By A t =K Fe l t b t It can be seen that if the tooth magnetic flux φ t , core stacking coefficient K Fe and core length l t unchanged, the tooth magnetic flux density B t Only with tooth width b t Therefore, if the tooth width is the same, it is beneficial to improve the utilization rate of the stator core. If the slot width is different and wider conductors are placed in the wider slot section, the slot fill rate will be improved.

[0061] Where: l k+1 is the width of the wider slot in the k+1th layer, l k is the width of the narrower slot in the kth layer, h k is the height of the narrow slot in the kth layer, Q is the number of stator slots, A t is the calculated cross-sectional area of ​​the tooth.

[0062] Among them, the step height of each layer of the stepped slot should be the height of two layers of conductors, ensuring that the cross-sectional area of ​​every two layers of coil conductors in the slot is the same, making it convenient for two adjacent layers of conductors to form a double-layer stacked winding or a double-layer wave winding, reducing the cost of motor processing and assembly.

[0063] In summary, in Example 1, the use of a stepped winding with a stainless steel protective layer can effectively reduce eddy current losses in the conductor near the air gap, thereby reducing the temperature rise of the conductor in this area. The stepped winding can also reduce the heat generated by copper loss and eddy current losses in the conductor near the air gap, resolving the problem of excessive local temperature rise in this area due to poor heat dissipation. In particular, the stepped winding with a stainless steel sheath and stepped or trapezoidal slot arrangement not only has the aforementioned advantages but also has a high slot fill rate and high core utilization. This improves the motor's efficiency, service life, and reliability.

[0064] Example 2

[0065] like Figure 1 As shown, in this embodiment 2, a stepped winding with a stainless steel protective layer is provided, which is applied to a trapezoidal slot core stator. In this embodiment, the stator slots contain eight layers of conductors, including a stator core 001, a stator trapezoidal slot 002, a main insulation layer 003, a conductor insulation layer 004, a stator tooth 005, the first and second layers of the widest conductors 006, the third and fourth layers of the widest conductors 007, the fifth and sixth layers of the narrow conductors 008 with stainless steel and phenolic resin protective layers, the seventh and eighth layers of the narrowest conductors 009 with stainless steel and phenolic resin protective layers, a phenolic resin layer 010, and a stainless steel protective layer 011.

[0066] In this embodiment, a stainless steel protective layer is provided on the effective conductor section of the 5th to 8th layers of conductors in the stator slots. The protective layer is perpendicular to the direction of the transverse leakage flux, thereby reducing the eddy current loss of the conductor in this area.

[0067] Select stainless steel material with weak magnetic conductivity, assuming the relative magnetic permeability is 75 and the electrical conductivity is 9.9×10 6 S / m, and the switching frequency of the power inverter is 4kHz, then the skin depth of the transverse leakage flux acting on the protective layer can be calculated to be 0.29mm. Therefore, taking the thickness of the protective layer as 0.3mm can effectively weaken the transverse leakage flux in the conductor, thereby reducing the eddy current loss in the conductor.

[0068] A phenolic resin layer is provided between the protective layer and the conductor. In this embodiment 2, the thickness of the phenolic resin layer is 0.5 mm. During the design calculation, the thickness of the phenolic resin layer can be determined according to the slot width, the conductor width and the thickness of the stainless steel protective layer. The phenolic resin layer is used to increase the rigidity of the stainless steel layer and isolate the heat conduction between the stainless steel layer and the conductor.

[0069] In this embodiment, the cross-sectional area of ​​the conductors of two adjacent layers is the same. Figure 1 As shown, each two adjacent layers of conductors are wound in double layers, connected in series to form a branch, and finally all branches are connected in parallel to form a phase winding, as shown in FIG. Figure 4 The figure shows the expanded diagram of the A-phase winding.

[0070] like Figure 6This is the expanded diagram of the stator A phase winding, as shown in Figure 7 The figure shows the equivalent circuit of the winding mentioned above. Since the voltage U AX If the total current carrying capacity of the winding I remains unchanged, the current of branches with different cross-sectional areas will be different, such as Figure 7 As shown, and by formula I k =U AX / R k ,R k =ρl / S k It can be seen that the current of the k-th layer winding is I k =U AX S k / ρl, so if it is assumed that the total length l of the conductors of each branch coil is the same, the smaller the cross-sectional area of ​​the conductor, the smaller the current flowing through it, that is, the current flowing through the conductor close to the air gap side is small.

[0071] Therefore, the total copper loss of the conductor close to the air gap is And the relationship between the copper loss of the i-th layer winding and the k-th layer is P Cui =S i / S k P Cuk Therefore, the heat generated by the copper loss of the conductor close to the air gap is small, which reduces the temperature rise of the conductor close to the air gap and improves the uneven temperature rise of the conductor in the stator slot.

[0072] Example 3

[0073] like Figure 2 As shown, in this embodiment 3, a stepped winding with a stainless steel protective layer is provided for use in a rectangular slot core stator, including a stator core 001, a stator trapezoidal slot 101, a main insulation layer 003, a conductor insulation layer 004, a stator tooth 005, a rectangular conductor 102, a stepped winding conductor with a stainless steel protective layer 008, a stepped winding conductor with a stainless steel protective layer 009, a phenolic resin layer 010, and a stainless steel side layer 011.

[0074] The motor stator slots contain eight layers of conductors. The two layers of conductors closest to the air gap are placed with conductors with stainless steel and phenolic resin protective layers. Conductors 008 and 009 are stepped windings with different effective current-carrying cross-sectional areas. The current-carrying cross-sectional areas of conductors 008 and 009 are also different from those of rectangular conductor 102. Rectangular conductor 102 is a conventional rectangular conductor with the same current-carrying cross-sectional area.

[0075] The stepped windings of conductors 008 and 009 with stainless steel protective layers and phenolic resin layers each use single-layer cross windings with a parallel branch number a=1. The conventional rectangular conductor 102 uses double-layer stacked windings for every two layers of conductors with a′=2 parallel branches.

[0076] If the motor is a three-phase four-pole 36-slot permanent magnet motor, then for the two layers of conductors 008 and 009, each layer of conductor adopts a single-layer cross winding form, then the number of slots per pole per phase is If the design is full pitch winding, the pitch The number of parallel branches is a=1, and the induced electromotive force of each branch is E φ1 =4.44fNk w1 φ1, where the fundamental pitch factor of the single-layer cross winding is Fundamental winding distribution factor Winding factor k w1 =k p1 ×k d1 , the main measured flux under each pole Series turns

[0077] Where: q is the number of slots per pole per phase, Q is the number of stator slots, p is the number of motor pole pairs, m is the number of motor phases, y1 is the winding intercept, τ is the motor pole pitch, a is the number of parallel branches, k w1 is the winding factor, k d1 is the winding fundamental wave distribution factor, k p1 is the fundamental pitch factor of the winding, N c is the number of coil turns.

[0078] For the remaining 6 layers of conventional rectangular conductors 102, each adjacent two layers of conductors adopt a full-pitch double-layer winding, so the number of slots per pole and per phase is If the design is full pitch winding, the pitch The number of parallel branches is a′=2, and the induced electromotive force of each branch is E′ φ1 =4.44f′N′k′ w1 φ1′, where the fundamental wave pitch factor of the single-layer cross winding is Fundamental distribution factor Winding factor k' w1 =k′ p1 k′ d1 , the main measured flux under each pole Series turns

[0079] Where: q' is the number of slots per pole per phase, p is the number of motor pole pairs, m is the number of motor phases, y1' is the winding intercept, τ' is the motor pole pitch, a' is the number of parallel branches, E' φ1 is the fundamental induced electromotive force of each phase winding, f' is the power frequency, N' is the total number of series turns of the winding, k' w1 Winding factor, k′ d1 is the winding fundamental wave distribution factor, k′ p1 is the fundamental wave pitch factor of the winding.

[0080] Therefore, the induced electromotive force of all branches composed of double-layer stacked windings and single-layer cross windings is the same, that is, E φ1 =E′ φ1 All branches are connected in parallel to form a single-phase winding, and no circulating current will be generated between the branches due to electromotive force imbalance.

[0081] like Figure 8 The figure shows the expanded diagram of phase A of the stepped winding with stainless steel sheath in the rectangular slot. Figure 9 As shown, the equivalent circuit of phase A of the stepped winding with stainless steel sheath in the rectangular slot is the same as that in the first embodiment. Since the voltage at each phase terminal is U AX However, due to the small current-carrying cross-sectional area and large resistance of the stepped winding, the current flowing through the stepped winding is small, the total copper loss and eddy current loss are small, and the heat generated is less, avoiding the problem of high temperature in this area and uneven temperature distribution of the conductor in the slot due to poor heat dissipation.

[0082] Example 4

[0083] The step winding with a stainless steel protective layer provided in this embodiment 4 is arranged in the step slot, such as Figure 3 As shown, it includes a stator core 001, a stator trapezoidal slot 201, a main insulating layer 003, a conductor insulating layer 004, a stator tooth 005, the 1st-2nd layer widest conductor 006, the 3rd-4th layer wide conductor 007, the 5th-6th layer narrow conductor 008 with a stainless steel and phenolic resin protective layer, the 7th-8th layer narrowest conductor 009 with a stainless steel and phenolic resin protective layer, a phenolic resin layer 010 and a stainless steel protective layer 011.

[0084] The stepped groove comprises four layers of steps, wherein each layer of the stepped groove can accommodate two layers of rectangular conductors with the same cross-sectional area.

[0085] The stepped groove contains a total of 8 layers of conductors.

[0086] The stepped groove, such as Figure 3 As shown, the stator slot is in the form of a ladder. The circumferential area of ​​the core near the stator yoke is larger, and a wide slot is set. The circumferential area of ​​the core near the air gap is smaller, and a narrow slot is set. The width of each step tooth is required to be equal, that is, b s1 =b s2 =...=b sn , by formula A t =K Fe l t b t It can be seen that if the tooth magnetic flux φ t , core stacking coefficient K Fe and core length l t unchanged, the tooth magnetic flux density B t Only with tooth width bt Therefore, if the tooth width is the same, the tooth slot width is different and the wider tooth slot is used to place the wider conductor, the slot fill factor will be improved and the core utilization will also be improved.

[0087] In this embodiment 4, a stainless steel protective layer is provided on the effective conductor section of the 5th to 8th layers of conductors in the stator slots. The protective layer is perpendicular to the transverse leakage flux direction to reduce the eddy current loss of the conductor in this area.

[0088] Select stainless steel material with weak magnetic conductivity, assuming relative magnetic permeability of 75 and electrical conductivity of 9.9×10 6 S / m, and the switching frequency of the power inverter is 4kHz, then the skin depth of the transverse leakage flux acting on the protective layer can be calculated to be 0.29mm. Therefore, taking the thickness of the protective layer as 0.3mm can effectively weaken the transverse leakage flux in the conductor, thereby reducing the eddy current loss in the conductor.

[0089] A phenolic resin layer is provided between the protective layer and the conductor. In Example 4, the thickness of the phenolic resin layer is 0.5 mm. During design calculations, the thickness of the phenolic resin layer can be determined based on the slot width, conductor width, and the thickness of the stainless steel protective layer. The phenolic resin layer serves to increase the rigidity of the stainless steel layer and isolate heat conduction between the stainless steel layer and the conductor.

[0090] like Figure 6 This is the expanded diagram of the stator A phase winding, as shown in Figure 7 The figure shows the equivalent circuit of the winding mentioned above. Since the voltage U AX If the total current carrying capacity of the winding I remains unchanged, the current of branches with different cross-sectional areas will be different, such as Figure 7 As shown, and by formula I k =I / R k ,R k =ρl / S k It can be seen that the current of the k-th layer winding is I k =IS k / ρl, so if it is assumed that the total length l of the conductors of each branch coil is the same, the smaller the cross-sectional area of ​​the conductor, the smaller the current flowing through it, that is, the current flowing through the conductor close to the air gap side is small.

[0091] Therefore, the total copper loss of the conductor close to the air gap is And the relationship between the copper loss of the i-th layer winding and the k-th layer is P Cui =S i / S k P Cuk Therefore, the heat generated by the copper loss of the conductor close to the air gap is small, which reduces the temperature rise of the conductor close to the air gap and improves the uneven temperature rise of the conductor in the stator slot.

[0092] Example 5

[0093] In this embodiment 5, a permanent magnet motor is provided. The inner rotor motor includes a motor stator having the stepped stator windings as described in embodiments 1, 2, 3, and 4.

[0094] Although the above describes the specific embodiments 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 solutions disclosed in the present invention without the need for creative work should be included in the scope of protection of the present invention.

Claims

1. A motor stator having a stepped winding with a protective layer and stepped slots, characterized in that: Each phase winding of the ladder winding includes N layers of coils radially distributed in the stator slots, and each phase winding includes at least N / 2 parallel branches. The current flowing through each parallel branch is different, but the current density in the conductors of each parallel branch is the same; all parallel branches are ultimately connected in parallel to form a phase winding, starting from the conductor closest to the air gap, and including at least one layer of stator winding with a protective layer, where N is an even number greater than or equal to 2.

2. The motor stator with a stepped winding and stepped slots with a protective layer according to claim 1, characterized in that: If the motor stator is a double-layer winding form, the conductor cross-sectional area of ​​the two adjacent layers of coils is the same, and the two adjacent layers of coils with the same conductor cross-sectional area constitute a winding branch; or, if the motor stator is a single-layer winding form, it contains at least two layers of coils with different conductor cross-sectional areas, and the at least two layers of coils with different conductor cross-sectional areas each constitute a winding branch.

3. The motor stator with the stepped winding and stepped slots with a protective layer according to claim 2, characterized in that: The conductors in the stator slots have different current-carrying cross-sectional areas, and the winding branches composed of the conductors with different current-carrying cross-sectional areas are ultimately connected in parallel.

4. The motor stator with stepped windings and stepped slots with a protective layer according to claim 2, characterized in that: Two adjacent layers of coils or one layer of coil with the same conductor cross-sectional area form a winding branch, and finally all branches are connected in parallel to form a phase winding. The induced electromotive force between all branches is the same.

5. The motor stator with stepped windings and stepped slots with a protective layer according to claim 1, characterized in that: The protective layer is perpendicular to the direction of the transverse leakage flux and is arranged on both sides of the conductor in the slot.

6. The motor stator with stepped windings and stepped slots with a protective layer according to claim 5, characterized in that: The thickness of the protective layer is greater than the skin depth when the transverse leakage flux frequency is f Wherein, μ is the magnetic permeability of the protective layer material, and σ is the electrical conductivity of the protective layer material.

7. The motor stator with a stepped winding and stepped slots with a protective layer according to claim 5 or 6, characterized in that: A phenolic resin layer is arranged between the protective layer and the conductor, and both the protective layer and the phenolic resin layer are only arranged on the effective conductor segment in the stator slot.

8. A permanent magnet motor, characterized in that: The motor stator comprises a stepped winding with a protective layer and stepped slots as claimed in any one of claims 1 to 7.

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