Slotless permanent magnet motor based on Halbach array

Abstract

The invention discloses a slotless permanent magnet motor based on a Halbach array, and belongs to the technical field of motor design and manufacturing. A rotor of the slotless permanent magnet motor is coaxially arranged in a stator, the stator comprises a stator iron core and a stator winding, the rotor comprises a permanent magnet and a rotor iron core, the permanent magnet is fixed on the outer wall of the rotor iron core and adopts a two-section Halbach array, the permanent magnet is composed of an auxiliary magnetic pole and a main magnetic pole, and an air gap is arranged between the stator iron core and the rotor. The stator winding is suspended in the air gap; during parallel magnetization, the magnetization directions of the permanent magnets of the Halbach array are along the tangential direction of the rotor, the magnetic pole directions are the same, and the main magnetic poles and the auxiliary magnetic poles both adopt a parallel magnetization mode; during radial magnetizing, the magnetizing direction of the permanent magnets of the Halbach array is in the radius direction of the rotor, the polarities of the adjacent permanent magnets are alternately arranged, the main magnetic poles adopt a radial magnetizing mode, and the auxiliary magnetic poles adopt a tangential magnetizing mode. According to the slotless permanent magnet motor, through directional magnetic field superposition of segmented magnetic poles, reverse magnetic leakage is reduced, air gap flux density is improved, and copper loss and iron loss are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of motor design and manufacturing, and in particular relates to a slotless permanent magnet motor based on a Halbach array. Background Art

[0002] Slotless motors have no stator slots, and the air gap magnetic field is evenly distributed. They have the advantages of small torque fluctuation, low iron loss, fast dynamic response, and simple structure. They are widely used in aerospace, medical equipment, new energy vehicles, industrial robots, precision industries and other fields.

[0003] Slotless motors are used in high-efficiency, precision, and lightweight scenarios. At present, with the continuous improvement of technology, slotless motors are more widely used, but there are still some shortcomings. The permanent magnets of slotless motors are surface-mounted radial magnetization, the magnetic field distribution is relatively scattered, and the effective air gap flux density is low. The magnetic field of the permanent magnets of the motor is not directionally enhanced, and part of the magnetic flux is reversely closed, resulting in material waste. In order to achieve the same output power, the motor needs to increase the air gap flux density or axial length, resulting in an increase in volume and a decrease in power density. The windings of slotless motors are located in the air gap area between the stator and the rotor because there is no slot to block them. They are directly exposed to the air gap magnetic field. The heat dissipation path relies on external cooling. Low air gap flux density requires higher current compensation power, resulting in increased copper loss. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems existing in the prior art and to provide a slotless permanent magnet motor based on a Halbach array.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The slotless permanent magnet motor based on the Halbach array includes a stator and a rotor. The rotor is coaxially arranged inside the stator. The stator includes a stator core and a stator winding. The rotor includes a permanent magnet and a rotor core. The permanent magnet is fixed on the outer wall of the rotor core and adopts a two-stage Halbach array. The permanent magnet consists of an auxiliary magnetic pole and a main magnetic pole. An air gap is provided between the stator core and the rotor, and the stator winding is suspended in the air gap. The permanent magnet has the following two magnetization methods, namely:

[0007] Parallel magnetization: The magnetization direction of the permanent magnets of the Halbach array is along the tangential direction of the rotor, the magnetic poles have the same direction, and both the main poles and the auxiliary poles are magnetized in parallel;

[0008] Radial magnetization: The magnetization direction of the permanent magnets of the Halbach array is along the radial direction of the rotor, the polarities of adjacent permanent magnets are arranged alternately, the main poles are magnetized radially, and the auxiliary poles are magnetized tangentially.

[0009] Furthermore, the permanent magnet is made of neodymium iron boron material.

[0010] Furthermore, the stator core is a cylinder formed by laminating high-conductivity silicon steel sheets.

[0011] Furthermore, the rotor core is formed by stacking silicon steel sheets.

[0012] Furthermore, in the two-stage Halbach array, the proportion of the main magnetic poles increases from 0.5 to 1, with an interval of 0.05.

[0013] Furthermore, the air gap magnetic flux density value ranges from 1.0 to 1.6T.

[0014] The beneficial effects of the present invention compared to the prior art are as follows: the Halbach array has unilateral magnetic concentration and sinusoidal magnetic field distribution, the two-stage Halbach array is conducive to the generation of sinusoidal back electromotive force, and has the advantages of simple structure, low processing and installation costs, etc. The slotless permanent magnet motor with a two-stage Halbach array structure proposed in the present invention reduces reverse leakage and improves air gap magnetic density by superimposing the directional magnetic field of the segmented magnetic poles; the magnetic field harmonics are offset and the torque fluctuation is further reduced; the magnetic flux utilization rate is improved, the copper loss and iron loss are reduced, and the motor efficiency is improved, but the manufacturing cost is increased. In addition, the slotless permanent magnet motor with a two-stage Halbach array has a concentrated magnetic field, allowing a wider air gap design and an enhanced heat dissipation effect.

[0015] The two segments in the two-segment Halbach refer to dividing the magnet arrangement structure of the Halbach array into two parts with different directions or phase angles, and further optimizing the magnetic field distribution through segmented design, enhancing the magnetic field strength in the target area and suppressing the leakage magnetic field on the non-working side. The two segments in the two-segment Halbach array in the present invention refer to permanent magnets with an initial magnetization direction difference of 90°, namely, the main magnetic pole and the auxiliary magnetic pole, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a working principle diagram of the slotless permanent magnet motor based on Halbach array of the present invention;

[0017] Figure 2 It is a schematic diagram of a standard two-stage Halbach array;

[0018] Figure 3 It is a schematic diagram of a radial Halbach array;

[0019] Figure 2 and Figure 3 In, R s -Outer radius of the model area, R o - Radius within the model area, R mo -Outer radius of the Halbach array permanent magnet, R mi-Inner radius of the Halbach array permanent magnet, R i -Rotor inner radius, μ r -Relative magnetic permeability, W m - Angle of the main magnetic pole, W p -Magnetic moment angle.

[0020] Figure 4 It is a simulation diagram of the slotless permanent magnet motor based on the Halbach array of the present invention;

[0021] Figure 5 It is the curve of the change of air gap magnetic flux amplitude;

[0022] Figure 6 It is the core loss variation curve.

[0023] The names and reference numerals of the components involved in the above drawings are as follows:

[0024] Stator core 1, stator winding 2, air gap 3, auxiliary magnetic pole 4, main magnetic pole 5, rotor core 6. DETAILED DESCRIPTION

[0025] like Figure 2-Figure 4 As shown, this embodiment discloses a slotless permanent magnet motor based on a Halbach array, including a stator and a rotor, the rotor is coaxially arranged inside the stator, the stator includes a stator core 1 and a stator winding 2, the rotor includes a permanent magnet and a rotor core 6, the permanent magnet is fixed on the outer wall of the rotor core 6 and adopts a two-segment Halbach array, the permanent magnet is composed of an auxiliary magnetic pole 4 and a main magnetic pole 5 (the segmented magnet is magnetized according to a characteristic angle, the air gap magnetic field is enhanced, and the back iron side leakage magnetic flux is weakened), an air gap 3 is provided between the stator core 1 and the rotor, and the stator winding 2 is suspended in the air gap 3; the permanent magnet has the following two magnetization methods, namely:

[0026] Parallel magnetization; the permanent magnets of the Halbach array are magnetized in the tangential direction of the rotor, and the magnetic poles are in the same direction. The main magnetic poles 5 and the auxiliary magnetic poles 4 are magnetized in parallel (the main magnetic poles 5 and the auxiliary magnetic poles 4 of the standard two-stage Halbach array are magnetized in parallel, which is called the standard two-stage Halbach array. The magnetization direction is tangential, and the magnetic poles are in the same direction);

[0027] Radial magnetization; the magnetization direction of the permanent magnets of the Halbach array is along the radial direction of the rotor, the polarities of adjacent permanent magnets are arranged alternately, the main magnetic pole 5 adopts radial magnetization, and the auxiliary magnetic pole 4 adopts tangential magnetization.

[0028] When magnetizing in parallel, the magnetization direction of the permanent magnet is tangential, the magnetic poles are in the same direction, and the magnetic field concentration is high. Through the Halbach array, a magnetic field close to a sine wave can be generated. The main magnetic pole 5 and the auxiliary magnetic pole 4 of the standard two-stage Halbach array are magnetized in parallel. The analytical model diagram is shown in the figure Figure 2 shown.

[0029] During radial magnetization, the magnetization direction of the permanent magnet is along the radial direction of the rotor, the polarities of adjacent permanent magnets are alternating, and the magnetic field path is direct, but the relative leakage flux is large and the magnetic energy utilization rate is low. The main magnetic pole 5 of the two-stage Halbach array of radial magnetization of permanent magnets adopts radial magnetization. The analytical model diagram is shown in the figure Figure 3 shown.

[0030] The slotless motor of the present invention adopts an inner rotor structure. The inner rotor is close to the motor axis. Heat can be directly conducted to the external heat dissipation system through the rotor shaft. The heat of the stator winding 2 can also be quickly dissipated through the casing to avoid heat accumulation. The moment of inertia is low and the dynamic response is fast.

[0031] Furthermore, the permanent magnet is made of neodymium iron boron material. Compared with samarium cobalt and neodymium iron boron, the permanent magnet material of the motor is neodymium iron boron, which has the advantages of ultra-high magnetic properties, reduced material consumption, high coercivity, high temperature stability, etc.

[0032] Furthermore, the stator core 1 is a cylinder with a smooth surface, and the stator core 1 is formed by stacking high-conductivity silicon steel sheets.

[0033] Furthermore, the rotor core 6 is made of laminated silicon steel sheets to reduce eddy current losses.

[0034] Furthermore, in the two-stage Halbach array, the proportion of the main magnetic pole 5 increases from 0.5 to 1, the interval is 0.05, and other parameters remain unchanged. The other parameters mainly refer to the dimensional parameters of the slotless motor other than the proportion of the main magnetic pole, such as the inner diameter, outer diameter, number of winding turns, magnetic pole thickness, air gap, axial length, etc.

[0035] The air gap flux density amplitude and the core loss of the motor of the two Halbach arrays are observed. When the proportion of the main magnetic pole 5 is high, the radial magnetic field component is enhanced, the air gap flux density amplitude is increased, and the torque density is improved; the increase in the air gap flux density amplitude leads to local saturation of the stator core 1 and increased iron loss; the auxiliary magnetic field of the parallel magnetization section is weakened, the sinusoidality of the air gap magnetic field waveform deteriorates, and the torque pulsation increases; the strong magnetic field of the main magnetic pole 5 may cause the local air gap magnetic field to reverse, increasing the risk of demagnetization.

[0036] Furthermore, the air gap magnetic flux density value ranges from 1.0 to 1.6T.

[0037] The air gap flux density value of the slotless permanent magnet motor ranges from 0.6 to 1.5 T. When the optimized design is not adopted, the air gap flux density value generally does not exceed 1 T. The air gap flux density value of the slotless permanent magnet motor using a two-stage Halbach array ranges from 1.0 to 1.6 T. Due to material limitations, it generally does not exceed 1.45 T.

[0038] The present invention optimizes the magnetic circuit of the slotless motor in combination with the Halbach array, improves the air gap flux density and other performances of the motor, and compares the simulation results of the standard parallel magnetization Halbach array and the main pole radial magnetization Halbach array through finite element simulation analysis, and changes the proportion of the main poles, compares the simulated air gap flux density and loss characteristics, and selects the magnetization method and main pole proportion with the best motor performance. The slotless permanent magnet motor based on the Halbach array proposed in this embodiment is a slotless motor with a two-stage Halbach array, which is as follows:

[0039] When the current of the slotless motor passes through the stator winding 2, an alternating magnetic field is generated. Due to the slotless structure, the magnetic field directly forms a closed loop in the air gap 3 between the stator core 1 and the rotor, without the need for magnetic conduction through the tooth slots. The permanent magnet generates a fixed magnetic field, which interacts with the stator magnetic field to form an electromagnetic torque. The working principle diagram of the motor is shown in the figure below. Figure 1 As shown in the figure, when the conduction mode is 2:2 conduction, the motor has 6 states in each cycle, the commutation interval is 60°, each phase winding is conducted 120° in each forward and reverse directions in each cycle, and at any time, only one high-voltage side switch and one lower low-voltage side switch of the three-phase bridge circuit are conducted. When the conduction mode is 3:3 conduction, the motor commutates once every 60° in one cycle, and each winding is conducted 180° in each forward and reverse directions in each cycle. If the air gap flux density waveform is a trapezoidal wave with a flat top width exceeding 120°, select the 2:2 conduction mode, and theoretically there is no torque fluctuation; if the air gap flux density waveform is a sine wave, the 3:3 conduction mode should be used.

[0040] The model of the slotless motor with two-stage Halbach array established in the simulation software is shown in the figure below. Figure 4 As shown, the Halbach array forms a highly concentrated and sinusoidal magnetic field on one side of the rotor by periodically arranging permanent magnets with different magnetization directions, and utilizes the magnetic field superposition effect, while the magnetic field on the other side is significantly weakened. The self-shielding effect of the Halbach array reduces the magnetic flux density of the rotor core 6, further reducing the eddy current loss and hysteresis loss of the rotor core 6.

[0041] Compared with conventional slotless motors, the present invention uses a two-stage Halbach array to optimize the permanent magnet. The Halbach array concentrates the magnetic field to the air gap side through the synergistic effect of the radial magnetization segment (main magnetic pole 5) and the tangential magnetization segment (auxiliary magnetic pole 4), weakens the magnetic field on the rotor back iron side, and improves the air gap magnetic flux density of the motor. Figure 5When magnetizing in parallel, the air gap flux density is the largest when the main pole duty ratio is 0.7; when magnetizing in radial direction, the air gap flux density is the largest when the main pole duty ratio is 0.95. In general, the air gap flux density amplitude during radial magnetization is between 1.0-1.2T, which is larger than the air gap flux density amplitude during parallel magnetization.

[0042] The slotless structure can eliminate stator teeth, reduce core eddy current and hysteresis losses, and the magnetic field focusing effect of the Halbach array reduces the rotor back iron magnetic density, which can further reduce rotor losses. The results are as follows: Figure 6 As shown in the figure, when parallel magnetization is performed, the core loss is the smallest when the duty ratio of the main magnetic pole is 0.65; when radial magnetization is performed, the core loss is the smallest when the duty ratio of the main magnetic pole is 0.95, and in general, the core loss during radial magnetization is smaller than the core loss during parallel magnetization.

[0043] The auxiliary magnetic poles of the two-stage Halbach can offset the demagnetization effect of the armature reaction on the main magnetic pole 5, improving the anti-demagnetization capability. The magnetic field enhancement and low loss characteristics make the motor smaller and lighter at the same power. The two-stage Halbach array only requires two magnetization directions, which is easier to assemble than the multi-stage Halbach array and reduces processing costs.

[0044] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A slotless permanent magnet motor based on a Halbach array, characterized in that: The invention comprises a stator and a rotor, wherein the rotor is coaxially arranged inside the stator, the stator comprises a stator core (1) and a stator winding (2), the rotor comprises a permanent magnet and a rotor core (6), the permanent magnet is fixed on the outer wall of the rotor core (6) and adopts a two-stage Halbach array, the permanent magnet consists of an auxiliary magnetic pole (4) and a main magnetic pole (5), an air gap (3) is provided between the stator core (1) and the rotor, and the stator winding (2) is suspended in the air gap (3); There are two ways to magnetize permanent magnets: Parallel magnetization; the magnetization direction of the permanent magnet of the Halbach array is along the tangential direction of the rotor, the magnetic pole direction is the same, and the main magnetic pole (5) and the auxiliary magnetic pole (4) are both magnetized in parallel; Radial magnetization; the magnetization direction of the permanent magnets of the Halbach array is along the radial direction of the rotor, the polarities of adjacent permanent magnets are arranged alternately, the main magnetic pole (5) adopts a radial magnetization method, and the auxiliary magnetic pole (4) adopts a tangential magnetization method.

2. The slotless permanent magnet motor based on Halbach array according to claim 1, characterized in that: The permanent magnet is made of neodymium iron boron material.

3. The slotless permanent magnet motor based on Halbach array according to claim 1, characterized in that: The stator core (1) is a cylinder formed by stacking high-conductivity silicon steel sheets.

4. The slotless permanent magnet motor based on Halbach array according to claim 1, characterized in that: The rotor core (6) is made of laminated silicon steel sheets.

5. The slotless permanent magnet motor based on Halbach array according to claim 1, characterized in that: In the two-stage Halbach array, the proportion of the main magnetic pole (5) increases from 0.5 to 1, with an interval of 0.

05.

6. The slotless permanent magnet motor based on Halbach array according to claim 1, characterized in that: The air gap magnetic flux density value ranges from 1.0 to 1.6T.

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