CN111682668B - Fractional slot brushless permanent magnet motor rotor yoke with inclined slots and slot size determining method - Google Patents

Fractional slot brushless permanent magnet motor rotor yoke with inclined slots and slot size determining method Download PDF

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CN111682668B
CN111682668B CN202010455953.2A CN202010455953A CN111682668B CN 111682668 B CN111682668 B CN 111682668B CN 202010455953 A CN202010455953 A CN 202010455953A CN 111682668 B CN111682668 B CN 111682668B
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slot
rotor yoke
permanent magnet
rotor
motor
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CN111682668A (en
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黄允凯
祝子冲
彭飞
夏雪
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Southeast University
Liyang Research Institute of Southeast University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/22—Rotating parts of the magnetic circuit
    • H02K1/27—Rotor cores with permanent magnets
    • H02K1/2706—Inner rotors
    • H02K1/272—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis
    • H02K1/274—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets
    • H02K1/2753—Inner rotors the magnetisation axis of the magnets being perpendicular to the rotor axis the rotor consisting of two or more circumferentially positioned magnets the rotor consisting of magnets or groups of magnets arranged with alternating polarity
    • H02K1/278—Surface mounted magnets; Inset magnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/14—Stator cores with salient poles
    • H02K1/146—Stator cores with salient poles consisting of a generally annular yoke with salient poles
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/12—Stationary parts of the magnetic circuit
    • H02K1/16—Stator cores with slots for windings
    • H02K1/165—Shape, form or location of the slots
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K1/00—Details of the magnetic circuit
    • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
    • H02K1/22—Rotating parts of the magnetic circuit
    • H02K1/28—Means for mounting or fastening rotating magnetic parts on to, or to, the rotor structures
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K3/00—Details of windings
    • H02K3/04—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors
    • H02K3/12—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors arranged in slots
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K3/00—Details of windings
    • H02K3/04—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors
    • H02K3/28—Layout of windings or of connections between windings
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K2213/00—Specific aspects, not otherwise provided for and not covered by codes H02K2201/00 - H02K2211/00
    • H02K2213/03—Machines characterised by numerical values, ranges, mathematical expressions or similar information

Abstract

The invention discloses a fractional slot high-speed brushless permanent magnet motor rotor yoke with a narrow slot inclined along the axial direction, and provides a method for determining the slot pitch and the slot depth of the inclined slot according to the matching of pole slots of a motor, the material characteristics, the running rotating speed and the winding connection mode. The structure is suitable for the fractional slot high-speed permanent magnet motor adopting a high-resistivity magnet and a sheath material, and the skewed slot rotor yoke provided by the invention is beneficial to reducing the rotor eddy current loss of the motor and expanding the rotating speed range of the motor. On the other hand, the proposed method for determining the size of the rotor yoke chute is universal and easy to integrate into existing motor design processes.

Description

Fractional slot brushless permanent magnet motor rotor yoke with inclined slots and slot size determining method
Technical Field
The invention relates to the technical field of brushless permanent magnet motors, in particular to a skewed slot rotor yoke of a high-speed brushless permanent magnet motor with a stator adopting fractional slot windings and a method for determining slot size.
Background
The high-speed brushless permanent magnet motor has the advantages of high power density, high efficiency, good dynamic characteristics and the like, and is widely applied to the fields of turbine machinery, high-speed lathes, flywheel energy storage, gas turbine power generation and the like. Owing to high rotor strength and excellent rotor dynamics, surface-mounted permanent magnet rotor structures are more common in high-speed brushless permanent magnet motors, and permanent magnets of the structure are attached to the surface of a rotor yoke. To improve structural reliability, high strength materials, such as carbon fiber composites and titanium aluminum alloys, are typically used to secure the permanent magnets to the rotor yoke.
Due to the presence of tooth harmonics, current harmonics and stator winding armature reaction magnetic potential harmonics, the magnetic field within the rotor is alternating, which generates eddy currents and corresponding losses in rotor conductive components. Particularly, in a brushless permanent magnet motor adopting a fractional slot winding, the number of slots of each phase of each pole is a fraction, and the sine degree of the armature reaction magnetic potential is poorer than that of the traditional integer slot distributed winding, and more harmonic components with larger amplitudes are contained. When the brushless permanent magnet motor runs at a high speed, the harmonic waves induce large eddy currents in the conductive rotor part, and generated eddy current loss is difficult to conduct out, so that high-temperature magnetic loss of the magnet can be caused. The eddy current loss of the rotor offsets the advantages of the brushless permanent magnet motor when fractional slots are adopted, and the rotating speed range of the brushless permanent magnet motor is limited. For a surface-mounted permanent magnet motor with a non-laminated structure, the eddy current loss generated by armature magnetic potential harmonic waves is more obvious.
The existing main measures for inhibiting the rotor eddy current of the brushless permanent magnet motor are as follows: the method comprises the steps of adopting a sheath and/or a permanent magnet material with low conductivity; a sheath and/or permanent magnet shaft/circumferential segment; and the shielding effect of the material with high conductivity and/or high magnetic conductivity is utilized to inhibit the rotor eddy current. The latter two methods can effectively reduce the eddy current loss of the rotor, but the related structure and process are complex, and simultaneously, the output torque and the structural strength of the rotor can be reduced, so that the method is only suitable for medium and high power motors.
The adoption of the sheath with high resistivity and the permanent magnet can reduce the eddy current loss of the rotor to a certain extent. However, when the fractional slot winding is adopted, the main component of the armature magnetic potential harmonic wave is close to the fundamental frequency, and the skin depth of the harmonic magnetic field is large, so that the harmonic magnetic field still enters the yoke part of the rotor. To enhance rotor stiffness, the rotor yoke is typically made of an electrically conductive alloy material in which alternating harmonic magnetic fields will generate large eddy current losses. The eddy current loss of the rotor and the temperature rise problem caused by the eddy current loss of the rotor are main factors for restricting further improving the power density and the fundamental wave frequency of the brushless permanent magnet motor.
Disclosure of Invention
The technical problem is as follows: the invention aims to provide a fractional-slot brushless permanent magnet motor rotor yoke structure with narrow slots inclined along the axial direction, so as to further reduce eddy current loss in the permanent magnet motor rotor yoke when high-resistivity jacket and magnet materials are adopted. Meanwhile, the invention provides a method for determining the size of the rotor yoke chute according to the matching of the pole slots of the motor, the running rotating speed, the material characteristics and the winding connection mode.
The technical scheme is as follows: the fractional slot brushless permanent magnet motor rotor yoke comprises a skewed slot, and comprises a stator core, a three-phase winding coil, a sheath, a permanent magnet and a rotor yoke, wherein the motor adopts a fractional slot concentrated winding structure, the rotor yoke is provided with skewed slots which are inclined along the axial direction, and the skewed slots are uniformly distributed along the circumference.
Furthermore, a rotor part of the motor adopts a surface-mounted magnet structure, and the sheath and the permanent magnet are made of high-resistivity materials.
Further, the permanent magnet is magnetized in a Halbach mode.
Furthermore, the rotor yoke is made of non-magnetic alloy material.
Furthermore, the chute is processed by adopting a linear cutting process, the width of the chute is 0.5mm, and the projection on the radial section of the rotor is rectangular.
A method of sizing a skewed slot on a rotor yoke of a fractional-slot brushless permanent magnet machine having skewed slots as described above, the method comprising the steps of:
step 1, drawing a waveform of a three-phase synthesized armature reaction magnetic potential according to a winding function of a fractional-slot concentrated winding motor, carrying out Fourier decomposition on the waveform to obtain a frequency spectrum of the armature reaction magnetic potential, and simultaneously determining a term with the lowest harmonic frequency and a term with the highest amplitude in the frequency spectrum;
step 2, the slot pitch s of the chute is the pole pitch p of an alternating magnetic field excited in a rotor yoke by the term with the maximum harmonic amplitude in the armature reaction magnetic potential spectrum;
and 3, the groove depth h of the inclined groove is twice the skin depth g of an alternating magnetic field excited in the rotor yoke by the item with the lowest harmonic frequency in the armature reaction magnetic potential frequency spectrum.
Further, when the skin depth of the term of the lowest harmonic order in the armature reaction magnetic potential spectrum exceeds 1/4 of the rotor yoke radius, the groove depth h of the diagonal groove is set to 1/2 of the rotor yoke radius.
Has the advantages that: the technical scheme provided by the invention has the advantages that:
the provided fractional slot high-speed brushless permanent magnet motor rotor yoke is provided with narrow slots which are inclined along the axial direction, the inclined slots cut off the flowing path of the alternating magnetic field of the rotor, thereby greatly reducing the eddy current loss on the rotor, being beneficial to reducing the temperature rise of the rotor of a fractional slot concentrated winding motor and expanding the rotating speed range of the motor;
the proposed method for determining the slot pitch and the slot depth is suitable for any pole slot matched fractional slot concentrated winding motor, and is independent of the phase number, the working mode and the topological structure of the brushless permanent magnet motor; the method can quickly and accurately determine the optimal slot pitch and the optimal slot depth, greatly simplifies the design process of the rotor yoke slot, and expands the space for selecting other electromagnetic parameters.
Drawings
FIG. 1 is an overall structure of a fractional-slot concentrated winding high-speed permanent magnet motor with a skewed rotor yoke according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a specific structure of a yoke part of the motor rotor in FIG. 1;
FIG. 3 is a portion of the rotor yoke of FIG. 2 in a flat, extended view along the outer rim;
FIG. 4 is a cross-sectional schematic view of the rotor yoke of FIG. 2;
FIG. 5 is a waveform diagram of the three-phase composite armature magnetic potential of the motor shown in FIG. 1;
fig. 6 is a spectrum diagram of the magnetic potential waveform of the armature of fig. 5.
Detailed Description
In order to make the objects, technical scheme features and advantages of the present invention clearer and more intuitive, the contents of the present invention are further described with specific embodiments in conjunction with the accompanying fig. 1 to 6.
The invention mainly aims to solve the problem of rotor eddy current loss when fractional slot concentrated windings are applied to a high-speed brushless permanent magnet motor, provides a fractional slot brushless permanent magnet motor rotor yoke structure with narrow slots inclined along the axial direction, and provides a method for determining the size of a rotor yoke chute.
Referring to fig. 1, a three-phase high-speed brushless permanent magnet motor 1 using fractional-slot concentrated winding has a pole number p of 10, a slot number z of 12, and a slot number q of each phase per pole of 2/5. The rated rotation speed n of the motor 1 is 15000r/min, and the electromagnetic fundamental frequency f is 1250 Hz. The coils 2 of the three-phase winding are wound around each tooth 31 of the stator core 3 individually, and the three-phase winding is supplied with three-phase alternating current from the inverter during normal operation. The motor rotor 4 is arranged in the stator core 3, and is of an inner rotor structure. The rotor is composed of a sheath 41, a permanent magnet 42, and a rotor yoke 43, and the rotor yoke 43 is connected to an output shaft of the motor 1. The sheath 41 is made of carbon fiber composite material, the permanent magnet 42 is a bonded neodymium iron boron magnet, the two materials have extremely high resistivity, and eddy current loss generated by armature reaction magnetic field harmonic waves in the two materials can be ignored. Each pole of permanent magnet 42 is formed by splicing three magnets and adopts a Halbach magnetizing mode.
The rotor yoke 43 is made of non-magnetic 304# stainless steel, the steel has excellent electrical conductivity, and a large eddy current and eddy current loss caused by the large eddy current are generated in the armature reaction magnetic field harmonic rotor yoke. To reduce this loss, the rotor yoke 43 is provided with axially inclined slots 431 on its outer periphery, which are uniformly distributed along the circumference, as shown in fig. 2, and these slots are obtained in the present embodiment by a wire cutting process.
For better clarity and visualization, fig. 3 shows a part of a planar development of the outer edge of the rotor yoke 43, in fig. 3, two parallel lines inclined are the contour lines of the inclined grooves 431 along the axial direction, and the distance between the projections of the two parallel lines on the radial cross section is the inclined groove width b, which is 0.35mm in this embodiment.
The dimensions of the chutes 431, including the chute distance s and the chute depth h, are obtained according to the following steps, as shown in fig. 3 and 4:
step 1, a winding function method is adopted to draw the waveform of the synthetic armature reaction magnetic potential of the permanent magnet motor with 10 poles and 12 slot fractional slot concentrated windings when three-phase sinusoidal current is introduced, as shown in fig. 5 (expressed by per unit value). The waveform was fourier decomposed to obtain an armature response spectrum, as shown in fig. 6. It should be noted that fig. 6 shows only harmonics of the order less than 60 and represents the magnitude of each harmonic in per unit. The lowest harmonic order and highest amplitude terms, in this embodiment the 1 st and 7 th harmonics, respectively, are determined from the spectrum.
Step 2, the slot pitch s of the skewed slots 431 is the pole pitch p of an alternating magnetic field excited in the rotor by the term (7 th harmonic) with the maximum harmonic amplitude in the armature reaction magnetic potential frequency spectrum:
s＝p＝πrou/7
wherein r isouIs the radius of the rotor yoke 43.
Step 3, the groove depth h of the inclined groove 431 is 2 times of the skin depth g of an alternating magnetic field excited in the rotor by a term (1 st harmonic) with the lowest harmonic frequency in the armature reaction magnetic potential frequency spectrum:
Figure BDA0002509235820000041
where f is the fundamental electromagnetic frequency of the motor (1250 Hz in this embodiment), μrIs a relative magnetic permeability, mu, of the rotor yoke 430For the vacuum permeability, σ is the electrical conductivity of the rotor yoke.
The embodiment adopts the skewed slot rotor yoke provided by the invention and the motor rotor designed according to the method for determining the skewed slot distance and the slot depth has greatly reduced total eddy current loss. Compared with the scheme without adopting the skewed slot rotor yoke, the total eddy current loss of the rotor is reduced by 42.5%, the heat dissipation of the rotor part of the fractional slot concentrated winding motor is favorably improved, and the rotating speed range of the motor application is expanded.
It should be understood that the above-described embodiments are merely illustrative of the present invention and are not intended to be exhaustive or limiting of the scope of the invention. After reading the present invention, various equivalent modifications of the core technical features of the present invention made by those skilled in the art fall within the scope of the present invention defined by the appended claims.

Claims (2)

1. A method for determining the size of an inclined slot on a rotor yoke of a fractional slot brushless permanent magnet motor with the inclined slot, wherein the motor comprises a stator core (3), three-phase winding coils (2), a sheath (41), a permanent magnet (42) and a rotor yoke (43), the rotor formed by the sheath (41), the permanent magnet (42) and the rotor yoke (43) is arranged in the stator core (3), the permanent magnet (42) is arranged in the sheath (41), the permanent magnet (42) and the sheath (41) are arranged on the outer surface of the rotor yoke (43) after being assembled, the three-phase winding coils (2) are arranged on the stator core (3), the three-phase winding coils (2) adopt a fractional slot concentrated winding structure, the rotor yoke (43) is provided with inclined slots (431) inclined along the axial direction, and the inclined slots are uniformly distributed along the circumference, and the method is characterized by comprising the following steps:
step 1, drawing a waveform of a three-phase synthesized armature reaction magnetic potential according to a winding function of a fractional slot concentrated winding, carrying out Fourier decomposition on the waveform to obtain a frequency spectrum of the armature reaction magnetic potential, and simultaneously determining a term with the lowest harmonic frequency and a term with the highest amplitude in the frequency spectrum;
step 2, the groove pitch of the inclined grooves (431)sPole pitch of alternating magnetic field excited in rotor yoke (43) for the term with the largest harmonic amplitude in armature reaction magnetic potential spectrump；
Step 3, the groove depth of the inclined groove (431)hSkin depth of alternating magnetic field excited in rotor yoke (43) for the lowest harmonic order term in armature reaction magnetic potential spectrumgTwice as much.
2. A method of dimensioning a skewed slot in a rotor yoke of a fractional slot brushless permanent magnet machine having skewed slots as claimed in claim 1, wherein the slot depth of the skewed slot (431) is such that the skin depth of the lowest harmonic term of the armature reaction potential spectrum exceeds 1/4 of the radius of the rotor yoke (43)hSet at 1/2 the radius of the rotor yoke.
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