Non-circular arc segment stator structure for weakening no-load back electromotive force distortion rate

Abstract

The application relates to the motor technical field and discloses a non-circular-arc-section stator structure for weakening no-load back electromotive force distortion rate, which comprises a non-circular-arc-section stator core body II, a plurality of stator core grooves are formed in the inner side of the non-circular-arc-section stator core body II, an armature winding is embedded in the stator core groove, a plurality of non-circular-arc-section stator core grooves are arranged on the outer ring of the non-circular-arc-section stator core body II, the groove bottom of the stator core groove corresponding to the non-circular-arc-section stator core groove is located on the connecting line between the non-circular-arc-section stator core groove and the inner ring center of the non-circular-arc-section stator core body II, the non-circular-arc-section stator core is periodically distributed in a 'convex arc section + groove arc section' mode, the groove arc section faces the groove bottom of the stator core groove, and the parameter optimization of the double-layer short-distance fractional-slot winding is combined, so that the no-load back electromotive force distortion rate is greatly reduced to 0.985%, the 3rd and 9th harmonics are completely eliminated, and the high-order harmonic content is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of motor technology, specifically to a non-circular arc segment stator structure that reduces the distortion rate of no-load back electromotive force. Background Technology

[0002] Defects and shortcomings of existing technology: The stator core teeth and slots of traditional automotive drive motors generally adopt a circular arc design. This structure has inherent magnetic circuit defects: From the perspective of reluctance effect, the air gap length between the circular arc tooth tip and the rotor surface will change periodically with the rotor rotation, causing the air gap magnetic flux to form a non-sinusoidal distribution of "reluctance pulsation" in the tooth tip region, which in turn excites low-order harmonics in the back electromotive force. At the same time, the reluctance characteristics of the circular arc slot are relatively weak, and some permanent magnet flux will form a leakage magnetic circuit through the slot (instead of being completely coupled to the winding through the stator teeth). The nonlinear distribution of leakage flux further destroys the sinusoidal nature of the back electromotive force. The strong magnetic flux environment exacerbates the flux concentration effect, which amplifies the back electromotive force waveform distortion problem.

[0003] To address the above issues, patent application number CN202110348569.7 and authorization announcement number CN113178997B discloses a method for suppressing back electromotive force (EMF) of a permanent magnet synchronous motor. The invention includes a permanent magnet motor rotor, wherein the rotor has at least two poles. When the harmonic order to be eliminated is n, an auxiliary slot is formed at the kτ / n position within a pair of pole pitches (within the -τ-τ range) to suppress the nth harmonic component. This invention employs a combination design of multiple auxiliary slot structures to suppress harmonic components of various low-order tooth harmonics with high content, thereby improving the sinusoidal nature of the back EMF. The width and depth of the auxiliary slots are set to 0.2mm-0.4mm, and the slot shape is a semi-circular slot, used to suppress back EMF harmonics in the permanent magnet synchronous motor.

[0004] However, the auxiliary slots are micro-slots, and the 0.2-0.4mm size requires strict machining accuracy, which is difficult for small and medium-sized manufacturers to meet. Multiple auxiliary slots require separate calculation of the slot positions for different harmonics and verification of inter-slot interference, resulting in a long design cycle. At the same time, the auxiliary slots increase the discontinuity of the rotor magnetic circuit, and local magnetic saturation may occur under long-term alternating magnetic field. Problems such as magnetic circuit stability need to be verified over a long period of time.

[0005] The invention patent document with application (patent) number CN202210258787.6 and authorization announcement number CN114598215B focuses on the quadrature axis (q-axis) back electromotive force, which is directly related to the motor torque. It accurately extracts the amplitude, frequency and initial phase of each order harmonic through Clarke transform, Park transform and Fourier transform, and then reconstructs the quadrature axis current according to the principle of "same frequency, same proportion, opposite phase". It can accurately cancel the original harmonics, and does not require complex multi-controller coordination or high-precision torque sensors. The operation logic is simple, the controller threshold is low, it is suitable for mainstream application scenarios of synchronous motors, and has wide versatility.

[0006] However, this invention relies too heavily on the measurement accuracy of the three-phase back electromotive force. If there is noise or error in the measurement, it will lead to distortion in the subsequent harmonic parameter extraction, affecting the suppression effect. Furthermore, the Fourier transform requires a certain data window, and its real-time performance is questionable under dynamic operating conditions where the motor speed changes rapidly. In addition, it only targets the q-axis harmonics and does not cover the direct axis (d-axis) harmonics. Long-term operation may affect the motor efficiency and temperature rise.

[0007] Therefore, a non-circular arc segment stator structure is proposed to reduce the distortion rate of the no-load back electromotive force. Summary of the Invention

[0008] The purpose of this invention is to provide a non-circular segment stator structure that reduces the distortion rate of the no-load back electromotive force, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force, comprising a non-circular arc segment stator core body II, wherein a plurality of stator core slots are formed on the inner side of the non-circular arc segment stator core body II, and an armature winding is embedded in the stator core slots;

[0010] The outer ring of the non-circular arc segment stator core body II is provided with a plurality of non-circular arc segment stator core grooves. The plurality of non-circular arc segment stator core grooves are equidistantly arranged along the circumference of the non-circular arc segment stator core body II. The bottom of the stator core groove corresponding to the non-circular arc segment stator core groove is located on the line connecting the center of the non-circular arc segment stator core groove and the center of the inner ring of the non-circular arc segment stator core body II.

[0011] In a non-circular arc segment stator structure according to the present invention for reducing the distortion rate of no-load back electromotive force, optionally, the non-circular arc segment stator core groove is composed of a plurality of non-circular arc segment stator core units II, wherein the non-circular arc segment stator core unit II includes two complete stator core slots and two half stator core slots, and the two half stator core slots are located at both ends of the non-circular arc segment stator core unit II.

[0012] In a non-circular arc segment stator structure according to the present invention for reducing the distortion rate of no-load back electromotive force, optionally, a non-circular arc segment stator core groove is formed at the splicing point of two adjacent non-circular arc segment stator core units II.

[0013] In a non-circular arc segment stator structure according to the present invention for reducing the no-load back electromotive force distortion rate, optionally, the amplitude of each harmonic of the back electromotive force is directly proportional to the winding coefficient of the armature winding, and the correlation model between the waveform distortion rate THD and the winding pitch is:

[0014] ;

[0015] In the formula, E v0 E represents the amplitude of the v-th harmonic electromotive force when the winding is a full-pitch condensed winding. 10 k is the amplitude of the fundamental electromotive force. w1 k is the fundamental winding coefficient. wV This represents the winding coefficient.

[0016] In a non-circular arc segment stator structure according to the present invention for reducing the distortion rate of no-load back EMF, optionally, the winding coefficient is jointly determined by the short-pitch coefficient and the distribution coefficient, which satisfies the formula:

[0017] ;

[0018] in, k pv for v Short-distance coefficient of subharmonics, k dv for v The distribution coefficient of the subharmonics.

[0019] In a non-circular arc segment stator structure according to the present invention for reducing the distortion rate of no-load back electromotive force, optionally, the ratio α of the armature winding pitch y to the pole pitch τ satisfies 0 < α ≤ 1, and specific harmonics are selectively suppressed by a short-pitch coefficient formula, wherein the short-pitch coefficient formula is: ;

[0020] Where v is the harmonic order.

[0021] In a non-circular segment stator structure according to the present invention, which reduces the distortion rate of the no-load back electromotive force, optionally, when k pv =0, the corresponding harmonic will be completely eliminated, at which point the following condition is met:

[0022] .

[0023] In a non-circular segment stator structure according to the present invention, which reduces the distortion rate of the no-load back electromotive force, optionally, the distribution coefficient... k dvDescribe the effect of armature winding distribution within stator core slots on harmonics. For a winding with q slots per pole per phase and a slot pitch angle of β, the distribution factor for the vth harmonic is:

[0024] ;

[0025] When the armature windings are arranged in a distributed manner, the distribution coefficient of higher harmonics decreases.

[0026] In a non-circular arc segment stator structure according to the present invention, which reduces the distortion rate of no-load back electromotive force, the armature winding is optionally a double-layer short-pitch armature winding.

[0027] In a non-circular arc segment stator structure according to the present invention for reducing the distortion rate of no-load back electromotive force, optionally, the groove of the non-circular arc segment stator core extends axially along the non-circular arc segment stator core body II, forming an axial ventilation and heat dissipation channel between the non-circular arc segment stator core body II and the motor housing.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention utilizes the periodic distribution of "protruding arc segments + grooved arc segments" in the non-circular arc segment stator core, with the grooved arc segments facing the bottom of the stator core slots. Combined with parameter optimization of the double-layer short-pitch fractional slot winding, the no-load back EMF distortion rate is significantly reduced to 0.985%, the 3rd and 9th harmonics are completely eliminated, and the content of higher harmonics is significantly reduced.

[0030] By matching the winding fundamental short-pitch coefficient with the stator magnetic circuit, the motor power output is stable without compromising the amplitude of the back EMF fundamental wave while achieving deep harmonic suppression.

[0031] The axial through groove of the non-circular arc segment of the stator creates a ventilation and heat dissipation channel between the stator and the motor housing, which accelerates heat dissipation, reduces copper and iron losses, and extends the service life of the motor.

[0032] By optimizing the structure to achieve "passive harmonic suppression", the motor does not need to rely on high-precision measurement or dynamic current adjustment. This results in smaller back EMF harmonic fluctuations and more stable operation under dynamic conditions such as acceleration and deceleration, making it suitable for hybrid excitation drive scenarios in new energy vehicles. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force according to the present invention.

[0034] Figure 2 This is a schematic diagram of the main structure of the stator core body II, which is composed of stator core unit II, in a non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force according to the present invention.

[0035] Figure 3 This is a schematic diagram of the stator core unit in a non-circular arc segment stator structure that reduces the distortion rate of no-load back electromotive force according to the present invention.

[0036] Figure 4 This is a three-dimensional structural diagram of the non-circular arc segment stator body II, which is composed of non-circular arc segment stator core unit II, in a non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force according to the present invention.

[0037] Figure 5 This is a schematic diagram of the main structure of a conventional circular stator core.

[0038] Figure 6 This is a schematic diagram of the main structure of the non-circular arc segment stator core body I, which is composed of non-circular arc segment stator core unit I in the control group.

[0039] Figure 7 This is a schematic diagram of the structure of the non-circular arc segment stator core unit I in the control group;

[0040] Figure 8 The no-load back electromotive force diagrams are for the conventional circular stator core body, the non-circular arc segment stator body I, and the non-circular arc segment stator body II.

[0041] Figure 9 Harmonic component diagrams corresponding to the no-load back electromotive force waveforms of a conventional circular stator, a non-circular arc segment stator body I, and a non-circular arc segment stator body II;

[0042] Figure 10 This is an exploded structural diagram of a non-circular arc segment stator structure that reduces the distortion rate of no-load back electromotive force according to the present invention applied to an electric motor.

[0043] In the figure: 1. Non-circular arc segment stator core body II; 2. Double-layer short-pitch armature winding; 3. Salient pole rotor core; 4. Electrically excited winding; 5. U-shaped permanent magnet; 6. Stator core teeth; 7. Stator core slot; 8. Circular stator core yoke; 9. Non-circular arc segment stator core unit I; 10. Non-circular arc segment stator core unit II; 11. Non-circular arc segment stator core groove. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0045] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0046] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0047] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0048] Example 1

[0049] Please see Figures 1 to 10 This embodiment provides the following technical solution:

[0050] A high distortion rate of the no-load back electromotive force can trigger a chain reaction of degradation effects across the electrical, mechanical, and material systems.

[0051] From the perspective of electromagnetic torque principle, the higher harmonics in the back electromotive force will cause the stator current to generate corresponding harmonic components. The harmonic current interacts with the air gap magnetic field to generate pulsating torque (the frequency of which is an integer multiple of the fundamental frequency). This torque is transmitted to the vehicle body through the transmission shaft system, causing vibration and noise in a specific frequency band, which damages the NVH performance of the whole vehicle.

[0052] From the perspective of energy loss, harmonic current will generate additional copper loss (because the effective value of harmonic current is involved in the Joule loss calculation) and iron loss (because the alternation frequency of higher harmonic magnetic fields is higher, and eddy current and hysteresis losses increase with the square of the frequency), which will lead to a decrease in the energy conversion efficiency of the motor and indirectly affect the vehicle's range.

[0053] From the perspective of insulation system reliability, harmonic voltage will generate high-frequency electric field impacts between the turns of the stator winding. Especially in flat wire motors, the small wire spacing will amplify this impact. At the same time, the temperature rise caused by harmonic losses will accelerate the thermal and electrical aging of the insulation material, significantly shortening the service life of the motor.

[0054] The waveform quality of the no-load back electromotive force (EMF) of a hybrid excitation motor is an important indicator for evaluating motor performance. Its harmonic content and waveform distortion rate directly affect the smoothness of motor operation, loss characteristics, and electromagnetic compatibility. Ideally, the back EMF should exhibit a sinusoidal waveform, but in actual motors, due to the non-ideal design of the armature winding and the stator core structure, harmonic components are inevitably generated.

[0055] In a conventional circular stator structure, the outer circle is a uniform arc, and the air gap permeability is only affected by the cogging effect. The permeability harmonics are mainly "characteristic tooth harmonics related to the number of slots and poles," leading to severe superposition of back electromotive force harmonics. Secondly, the stator's outer arc surface design, which is tightly fitted to the motor housing, lacks heat dissipation ventilation channels, which is not conducive to the motor's heat dissipation and increases losses.

[0056] The present invention provides a non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force, including a non-circular arc segment stator core body II1, a plurality of stator core slots 7 are opened on the inner side of the non-circular arc segment stator core body II1, and an armature winding 2 is embedded in the stator core slots 7. The armature winding 2 adopts a double-layer short-pitch armature winding.

[0057] The outer ring of the non-circular arc segment stator core body II1 is provided with a number of non-circular arc segment stator core grooves 11. The number of non-circular arc segment stator core grooves 11 are equidistantly arranged along the circumference of the non-circular arc segment stator core body II1. The bottom of the stator core groove 7 corresponding to the non-circular arc segment stator core groove 11 is located on the line connecting the center of the non-circular arc segment stator core groove 11 and the center of the inner ring of the non-circular arc segment stator core body II1.

[0058] Among them, the non-circular arc segment stator core groove 11 is composed of several non-circular arc segment stator core units II 10. The non-circular arc segment stator core unit II 10 includes two complete stator core slots 7 and two half stator core slots 7, and the two half stator core slots 7 are located at both ends of the non-circular arc segment stator core unit II 10.

[0059] At the joint of two adjacent non-circular arc stator core units II10, a non-circular arc stator core groove 11 is formed. The non-circular arc stator core groove 11 extends axially along the non-circular arc stator core body II1, forming an axial ventilation and heat dissipation channel between the non-circular arc stator core body II1 and the motor housing.

[0060] By setting the outer ring of the non-circular arc segment stator core body II1 as petal-shaped, and equidistantly arranged grooves 11 of the non-circular arc segment stator core body II1 around the circumference, the outer ring of the non-circular arc segment stator core body II1 forms a periodic distribution of "protruding arc segment + groove arc segment", which actively controls the spatial harmonic components of the air gap magnetic permeability. The fundamental frequency of the magnetic permeability harmonic changes from "high order related to the number of slots" to "low order related to the number of petals", so that the high order magnetic permeability harmonics are concentrated.

[0061] By combining the short-pitch coefficient of the armature winding, "cancellation coupling between magnetic permeation harmonics and winding harmonics" can be achieved, suppressing harmonic generation at its source. Furthermore, the periodic distribution of "raised arc segments + grooved arc segments" not only reduces and weakens the back EMF harmonic content but also increases heat dissipation and ventilation channels. The groove 11 design of the non-circular arc segment stator core at the junction of the non-circular arc segment stator core units II10 accelerates airflow, effectively dissipating the heat generated by the motor stator, reducing motor losses, and improving motor stability and service life.

[0062] The present invention designs a non-circular arc segment stator structure that reduces the distortion rate of no-load back electromotive force, which is applied to an 8-pole 36-slot double-layer winding structure embedded U-shaped permanent magnet and salient pole electromagnetic hybrid excitation motor. The motor includes a non-circular arc segment stator core body II, a double-layer short-pitch armature winding 2, a salient pole rotor core 3, an electric excitation winding 4, and a U-shaped permanent magnet 5. The U-shaped permanent magnet 5 is composed of three rectangular permanent magnets, with the middle one being larger and the two sides smaller, forming a U-shaped composite permanent magnet.

[0063] When the motor is running, three-phase alternating current is supplied to the double-layer short-pitch armature winding 2. The alternating magnetic field generated by the three-phase alternating current interacts with the U-shaped permanent magnet 5, generating electromagnetic torque (including permanent magnet torque and reluctance torque) according to the left-hand rule, which drives the rotor to rotate and drives the load to operate. The addition of the electrically excited winding 4 can adjust the air gap magnetic flux in real time according to the load demand: when the load increases, the magnetization is increased to improve the torque; when the speed increases, the magnetization is weakened to widen the speed regulation range.

[0064] This invention systematically analyzes the influence mechanism of armature winding and non-circular arc segment stator core on no-load back electromotive force harmonics and total harmonic distortion (THD), establishes a theoretical correlation model and derives key calculation formulas. The harmonic characteristics of the back electromotive force can be described by Fourier series expansion. The instantaneous value expression of the no-load back electromotive force is:

[0065] ;

[0066] E1 is the fundamental frequency amplitude, Ev is the vth harmonic amplitude, and ω is the electrical angular frequency. v represents the phase of the vth harmonic.

[0067] Waveform distortion rate (THD) is defined as the ratio of the square root of the sum of the squares of the effective values ​​of each harmonic to the effective value of the fundamental frequency.

[0068] .

[0069] Armature winding pitch is a key parameter affecting the back electromotive force waveform. Specific harmonics are suppressed through harmonic modulation of the winding coefficient. The winding coefficient is determined by both the short-pitch coefficient and the distribution coefficient, and satisfies the following formula:

[0070] ;

[0071] in, k pv for v Short-distance coefficient of subharmonics, k dv for v The distribution coefficient of the subharmonics.

[0072] Winding pitch y (usually expressed as a fraction of pole pitch τ, i.e.) ,0< ≤1) Selective suppression of harmonics is achieved through the short-distance coefficient. The formula for the short-distance coefficient is: ;

[0073] Where v is the harmonic order.

[0074] then k pv =0, the corresponding harmonic will be completely eliminated, at which point the following condition is met:

[0075] ;

[0076] Distribution coefficient k dv Describe the effect of the armature winding 2 distribution within the stator core slot 7 on harmonics. For a winding with q slots per pole per phase and a slot pitch angle of β, the distribution coefficient of the vth harmonic is:

[0077] ;

[0078] When the armature winding 2 is arranged in a distributed manner, the distribution coefficient of higher harmonics is significantly reduced.

[0079] The amplitudes of each harmonic of the back electromotive force are directly proportional to the winding coefficient of the armature winding (2), i.e. E v ∝ k wv The correlation model between waveform distortion rate (THD) and winding pitch is as follows:

[0080] ;

[0081] In the formula, E v0 E represents the amplitude of the v-th harmonic electromotive force when the winding is a full-pitch condensed winding. 10 k is the amplitude of the fundamental electromotive force. w1 k is the fundamental winding coefficient. wV As the winding coefficient, by optimizing the pitch α, the k of a specific harmonic can be made... wV =0, thus significantly reducing waveform distortion rate (THD).

[0082] Based on the above, the motor of the present invention adopts 8 poles (p=4 pole pairs), 36 slots (Z=36 slots), and three phases (m=3 phases).

[0083] The number of slots per pole per phase is: q = Z / 2mp = 36 / 2 × 3 × 4 = 1.5, which belongs to fractional slot winding (the number of slots per pole per phase q is not an integer, and it has the natural advantages of high fundamental winding coefficient and low harmonics).

[0084] The winding pitch y = 3 slots, and the pole pitch τ = Z / 2p = 36 / 8 = 4.5 slots;

[0085] The shortest distance ratio α = y / τ = 3 / 4.5 = 2 / 3;

[0086] The suppression effect on different harmonic orders can be accurately calculated based on the short-distance coefficient formula:

[0087] 3rd harmonic (v=3): k p3 =sin(3·π / 2·2 / 3)=sinπ=0;

[0088] This means that the winding's ability to induce the third harmonic is "zero". Even if the air gap magnetic flux density contains the third harmonic, it is impossible to generate the third harmonic back electromotive force in the winding.

[0089] 9th harmonic (v=9): kp9=sin(9·π / 2·2 / 3)=sin3π=0;

[0090] Similarly, the 9th harmonic is completely suppressed;

[0091] Fundamental wave (v=1): kp1=sin(1·π / 2·2 / 3)=sin3π≈0.866;

[0092] The fundamental winding coefficient is relatively high to ensure sufficient back electromotive force fundamental amplitude, taking into account both "harmonic suppression" and "fundamental output".

[0093] Example 2

[0094] The only difference between this embodiment and Embodiment 1 is that the stator core constituting the motor includes a non-circular arc segment stator core body I, which is composed of several non-circular arc segment stator units I9. The non-circular arc segment stator I includes three complete stator core slots 7. The stator core teeth 6 corresponding to the non-circular arc segment stator core grooves 11 are located on the line connecting the inner circle center of the non-circular arc segment stator core grooves 11 and the non-circular arc segment stator core body I1. The arc segment dimensions and stator core slot 7 dimensions in the non-circular arc segment stator core body I are the same as the arc segment dimensions and stator core slot 7 dimensions in the non-circular arc segment stator core body II.

[0095] Example 3

[0096] like Figure 5As shown, in this embodiment, the stator core constituting the motor adopts a conventional circular stator core, and the size of its stator core slot 7 is consistent with the stator core slot 7 in the non-circular arc segment stator core body II.

[0097] By establishing motor models with circular stators, non-circular arc segment stators I and non-circular arc segment stators II, and using finite element simulation, the no-load induced electromotive force waveforms of circular stators, non-circular arc segment stators I and non-circular arc segment stators II were obtained.

[0098] like Figure 8 As shown, the three no-load back electromotive forces in the figure are subjected to Fourier transform, and the content of each odd harmonic is obtained according to the formula:

[0099] .

[0100] The calculated waveform distortion rate (THD) values ​​for the three waveforms are shown in the table below:

[0101]

[0102] Based on the harmonic content in the table, draw... Figure 9 Harmonic component diagrams corresponding to the no-load back electromotive force waveforms of conventional circular stator, non-circular arc segment stator I and II;

[0103] Analysis and calculation show that the waveform distortion rate of the no-load back EMF of the circular stator is 5.091%, the waveform distortion rate of the no-load back EMF of the non-circular segment stator I is 5.184%, and the waveform distortion rate of the no-load back EMF of the non-circular segment stator II is 0.985%. Compared with the circular stator and the non-circular segment stator I, the waveform distortion rate of the no-load back EMF of the non-circular segment stator II is significantly reduced. Therefore, the non-circular segment stator structure of this invention has a significant weakening effect on the waveform distortion rate of the no-load back EMF.

[0104] All parts not described in this invention are the same as or can be implemented using existing technology. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force, characterized in that, The stator core body II (1) includes a non-circular arc segment. The inner side of the non-circular arc segment stator core body II (1) is provided with a plurality of stator core slots (7), and an armature winding (2) is embedded in the stator core slots (7). The outer ring of the non-circular arc segment stator core body II (1) is provided with a plurality of non-circular arc segment stator core grooves (11). The plurality of non-circular arc segment stator core grooves (11) are equidistantly arranged along the circumference of the non-circular arc segment stator core body II (1). The bottom of the stator core groove (7) corresponding to the non-circular arc segment stator core groove (11) is located on the line connecting the center of the inner ring of the non-circular arc segment stator core groove (11) and the non-circular arc segment stator core body II (1). The non-circular arc segment stator core groove (11) is composed of several non-circular arc segment stator core units II (10). The non-circular arc segment stator core unit II (10) includes two complete stator core slots (7) and two half stator core slots (7), and the two half stator core slots (7) are located at both ends of the non-circular arc segment stator core unit II (10). The amplitude of each harmonic of the back electromotive force is directly proportional to the winding coefficient of the armature winding (2). The correlation model between the waveform distortion rate (THD) and the winding pitch is as follows: ； In the formula, E v0 E represents the amplitude of the v-th harmonic electromotive force when the winding is a full-pitch condensed winding. 10 k is the amplitude of the fundamental electromotive force. w1 k is the fundamental winding coefficient. wV For winding coefficients; The winding factor is determined by both the short-pitch factor and the distribution factor, and it satisfies the following formula: ； Where, k pv Let k be the short-distance coefficient of the v-th harmonic. dv The distribution coefficient of the vth harmonic; The ratio α of the pitch y to the pole pitch τ of the armature winding (2) satisfies 0 < α ≤ 1, and specific harmonics are selectively suppressed by the short-pitch coefficient formula, which is: Where v is the harmonic order; At that time, k pv =0, the corresponding harmonic will be completely eliminated, at which point the following condition is met: ； Distribution coefficient k dv Describe the effect of the armature winding (2) distribution in the stator core slot (7) on harmonics. For a winding with q slots per pole per phase and a slot pitch angle of β, the distribution coefficient of the vth harmonic is: ； When the armature winding (2) is arranged in a distributed manner, the distribution coefficient of higher harmonics decreases; The armature winding (2) is a double-layer short-pitch armature winding; the non-circular arc segment stator core groove (11) is axially connected along the non-circular arc segment stator core body II (1), forming an axial ventilation and heat dissipation channel between the non-circular arc segment stator core body II (1) and the motor housing.

2. The non-circular arc segment stator structure for reducing the distortion rate of no-load back electromotive force according to claim 1, characterized in that: The non-circular arc segment stator core groove (11) is formed at the splicing point of two adjacent non-circular arc segment stator core units II (10).

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