Method for modulating air gap harmonics of permanent magnet motor by designing and editing magnetic field through salient poles between rotor poles

Abstract

The invention relates to the technical field of motor technologies, in particular to a method for editing magnetic field modulation permanent magnet motor air gap harmonic waves through rotor inter-pole salient pole design, and the method comprises the steps: analyzing the internal relation between torque and magnetic field harmonic waves according to an analytic expression of the output torque of a magnetic field modulation permanent magnet motor; analyzing the total contribution of each harmonic to the output torque, and analyzing the unit contribution ratio of each harmonic to the torque; according to different unit contribution ratios of harmonic waves to output torque, a harmonic wave editing thought is determined, that is, a low-contribution-ratio harmonic wave amplitude is sacrificed to improve a high-contribution-ratio harmonic wave amplitude; according to a harmonic wave editing thought, a rotor inter-pole salient pole design is adopted, air gap magnetic resistance is adjusted, and a target magnetic field harmonic wave amplitude is directionally edited; and finally, analyzing the zero-load back electromotive force amplitude and the average output torque value of the motor, and verifying the harmonic editing result. Air gap harmonic waves of the magnetic field modulation permanent magnet motor are edited through rotor inter-pole salient pole design, and the output torque of the magnetic field modulation permanent magnet motor is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to a method for editing magnetic field modulation air gap harmonics of a permanent magnet motor by designing rotor inter-pole salient poles. Background Art

[0002] Energy and environmental issues are becoming increasingly prominent, prompting people to seek more efficient and environmentally friendly ways of energy utilization. Against this background, permanent magnet synchronous motors have emerged as an effective way to solve energy and environmental problems. Permanent magnet synchronous motors, with their high efficiency and low energy consumption, significantly reduce energy waste. Compared with traditional motors, they have higher average efficiency over the entire speed range, which helps to reduce energy consumption. High efficiency means less energy waste and lower carbon emissions, which is of great significance for mitigating global climate change. Permanent magnet synchronous motors use advanced permanent magnet materials and electronic control technology, representing the innovative direction of motor technology. Therefore, permanent magnet synchronous motors play an important role in solving energy and environmental problems.

[0003] The magnetic field modulation permanent magnet motor is a special type of permanent magnet synchronous motor. Due to the magnetic field modulation effect, the motor has better performance. The magnetic field modulation motor can generate higher torque in the same volume through a special magnetic field design, which means that the volume of the magnetic field modulation motor can be smaller at the same power output, or it can provide greater power output at the same volume; the magnetic field modulation technology enables the motor to maintain high efficiency at different speeds and has a wider speed regulation range. Compared with traditional permanent magnet synchronous motors, it can provide better performance at both low and high speeds; due to the characteristics of magnetic field modulation, the vibration and noise of this type of motor during operation are usually lower than those of traditional permanent magnet synchronous motors. This makes the magnetic field modulation motor have obvious advantages in applications requiring low noise and vibration; in some applications that run at high speed or require a wide range of speed regulation, the magnetic field modulation motor exhibits superior weak magnetic control capabilities, which helps the motor maintain stable performance at high speeds; magnetic field modulation motors are usually used in conjunction with advanced control strategies, which can further improve the dynamic response and steady-state performance of the motor, making it advantageous in some high-precision, high-dynamic response applications.

[0004] The applicant found that the working principle of the magnetic field modulation permanent magnet motor is different from that of the traditional permanent magnet synchronous motor, and the harmonic content in the motor air gap is richer. However, how to better utilize the positive effect of magnetic field harmonics has always been the key difficulty of the magnetic field modulation permanent magnet motor. In addition, the study found that there are obvious differences in the contribution of motor magnetic field harmonics to the output torque. Therefore, how to deeply identify the high-contribution harmonic orders, edit the magnetic field harmonics, and improve the output torque is the focus of current research. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose a method for editing the air gap harmonics of a magnetic field modulated permanent magnet motor by designing the salient poles between the rotor poles, so as to solve the problem that the existing magnetic field modulated permanent magnet motor cannot make good use of the positive effects of the magnetic field harmonics, resulting in difficulty in identifying high-contribution harmonic orders and editing the magnetic field harmonics to improve the output torque.

[0006] Based on the above purpose, the present invention provides a method for editing the air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles, comprising the following steps:

[0007] Step S1, analyzing the intrinsic relationship between torque and magnetic field harmonics according to the analytical expression of motor output torque, and locating air gap magnetic field harmonics as the key to analyzing the method of improving torque;

[0008] Step S2, according to the analytical formula of air gap magnetic flux density, determine two key parameters affecting magnetic flux density: permanent magnet magnetomotive force and air gap magnetic permeability;

[0009] Step S3, ignoring the magnetic field generated by the armature winding on the stator and the tooth slot structure on the stator, only considering the magnetic flux path formed by the permanent magnetic field generated by the permanent magnet on the rotor, so as to select the basic unit of the rotor structure according to the symmetry and periodicity of the rotor magnetic circuit, and establish the analytical formula of the permanent magnet magnetomotive force;

[0010] Step S4, simulating the magnetic flux path of the permanent magnet of the motor under the influence of the complex stator structure, establishing a fine mathematical model of the air gap permeance of the high-order harmonics, selecting the basic unit of the tooth slot structure on the stator, and establishing an analytical formula of the air gap permeance according to the mathematical model of the air gap permeance;

[0011] Step S5, programming the calculation expression of the air gap magnetic density through MATLAB to obtain the waveform diagram of the air gap magnetic density, perform Fourier decomposition on the waveform of the air gap magnetic density, obtain the harmonic content diagram of the motor air gap magnetic density, study the contribution of each harmonic in the air gap magnetic field to the output torque, and analyze the contribution ratio of each harmonic per unit to the output torque;

[0012] Step S6, based on the contribution ratio of each harmonic per unit to the output torque, determine a harmonic editing strategy of reducing the amplitude of high-order harmonics with low contribution ratios and increasing the amplitude of low-order harmonics with high contribution ratios;

[0013] Step S7, the goal of harmonic editing is achieved by designing salient poles between rotor poles, the amplitude of high-order harmonics with low contribution ratio is reduced, and the amplitude of low-order harmonics with high contribution ratio is increased, so that both no-load back electromotive force and output torque are improved.

[0014] Preferably, in step S1, without considering magnetic field saturation, the analytical expression of the theoretical average output torque is as follows:

[0015]

[0016] Where, m represents the number of motor phases, I n Represents the input current amplitude, E A Represents the no-load back EMF amplitude, n s is the number of turns per phase of the motor winding, l stk Represents the axial length of the motor, N a represents the number of modulation poles on the armature teeth, t sp represents the modulation tooth arc, w s Represents the modulated inter-tooth arc, R s Represents the motor air gap radius, w o Represents the arc of the notch, P r is the number of permanent magnet poles of the motor, Z f is the number of motor modulation teeth, ω r is the rotor angular velocity of the motor, B represents the air gap flux density of the motor, and nj is defined as follows:

[0017]

[0018] From the above analytical formula of output torque, it can be found that the air gap magnetic flux B of the motor is the key parameter affecting the output torque. Therefore, to analyze the output torque, it is necessary to first analyze the air gap magnetic field of the motor and analyze the influence of the harmonic content of the air gap magnetic flux and the harmonic amplitude on the output torque.

[0019] Preferably, in step S2, the analytical formula of the air gap magnetic flux density is as follows:

[0020] B(θ s ,t)=F(θ s ,t)×Λ(θ s )

[0021] Among them, F is the permanent magnet magnetomotive force, Λ is the air gap magnetic permeance. From the analytical formula of the air gap magnetic density, it can be found that to analyze the air gap magnetic density, it is necessary to first analyze the magnetomotive force function of the rotor permanent magnet and the stator air gap magnetic permeability function of the motor.

[0022] Preferably, in step S3, an analytical model of the magnetomotive force corresponding to the permanent magnet of a unit module of the rotor is established, and an analytical formula of the permanent magnet magnetomotive force is obtained according to the analytical model as follows:

[0023]

[0024]

[0025] Among them, F i is the harmonic amplitude of the i-th order magnetomotive force, α p is the permanent magnet pole arc coefficient, F m It can be expressed as:

[0026]

[0027] Among them, B r is the remanence of the permanent magnet, μ0 is the vacuum permeability, μ r is the relative magnetic permeability of the permanent magnet, h m is the thickness of the permanent magnet.

[0028] Preferably, in step S4, the magnetic flux path and permeance model diagram of the stator modulation tooth in a unit module can be expressed as follows based on the analytical model:

[0029]

[0030] Where Λ0 is the DC component of the air gap permeability, Λ i is the i-th air gap permeability harmonic amplitude, Λ0 and Λ i It can be expressed as:

[0031]

[0032] Preferably, in step S5, the following sub-steps are also included:

[0033] Step S5.1, selecting working harmonics from the harmonic content diagram of the motor air gap magnetic flux density, the working harmonics include low-order harmonics of 2nd, 3rd, 9th, 11th, and high-order harmonics of 32nd;

[0034] Step S5.2, calculate the contribution of each harmonic of the air gap magnetic density to the output torque based on the analytical expression of the motor output torque, and obtain the contribution of each harmonic order to the output torque. From the contribution of each harmonic order, it can be obtained that the contribution of the low-order 2nd and 3rd harmonics to the output torque is greater than the contribution of the high-order 32nd harmonic to the output torque.

[0035] Preferably, in step S6, based on the contribution of each order of air gap magnetic density to the output torque, the contribution of each harmonic per unit to the output torque is calculated, that is, the contribution ratio of each harmonic is calculated. From the contribution ratio of each harmonic, it can be concluded that the contribution ratio of the 2nd and 3rd harmonics is greater than that of other harmonics. Therefore, the output torque of the motor can be improved by reducing the amplitude of high-order harmonics with low contribution ratio and increasing the amplitude of low-order harmonics with high contribution ratio.

[0036] Preferably, in step S7, the following sub-steps are also included:

[0037] Step S7.1, based on the contribution ratio of each unit harmonic to the torque, the harmonic editing idea is to reduce the amplitude of high-order harmonics with low contribution ratio and increase the amplitude of low-order harmonics with high contribution ratio;

[0038] Step S7.2, analyzing the air gap magnetic field analytical model of the motor model using the rotor inter-pole salient pole design, it can be found that the inter-pole salient pole design is adopted by introducing the structural characteristics of the rotor editing magnetic field harmonics;

[0039] Step S7.3, comparing the air gap magnetic flux harmonics of the motor with the rotor inter-pole salient pole design and the motor with the traditional design, it can be found that the amplitudes of the second and third harmonics in the air gap magnetic field of the motor with the rotor inter-pole salient pole design are improved, while the amplitude of the 32nd harmonic is reduced;

[0040] Step S7.4, comparing the contribution of each harmonic of the air gap magnetic flux density to the output torque of the motor using the salient pole design between the rotor poles and the motor using the traditional design, it can be found that the magnetic field harmonics are edited by using the method of designing the salient pole between the rotor poles, thereby improving the low-order 2nd and 3rd harmonics that have a high contribution to the output torque and reducing the amplitude of the high-order 32nd harmonic that has a low contribution to the output torque;

[0041] Step S7.5, by comparing the no-load back-electromotive force fundamental amplitudes of the motor with salient poles designed between the rotor poles and the motor with traditional design, it can be obtained that the no-load back-electromotive force of the motor can be improved by using the method of editing the magnetic field harmonics by using the salient pole design between the rotor poles. By comparing the average output torque and torque pulsation of the motor with salient poles designed between the rotor poles and the motor with traditional design, it can be obtained that the average output torque of the motor can be improved by using the method of editing the magnetic field harmonics by using the salient pole design between the rotor poles. This verifies the feasibility of improving the output torque by editing the air gap harmonics of the magnetic field modulation permanent magnet motor through the salient pole design between the rotor poles.

[0042] The beneficial effects of the present invention are as follows:

[0043] 1. The present invention analyzes the output torque analytical expression of the magnetic field modulated permanent magnet motor, deeply analyzes the contribution of each harmonic to the output torque, quantitatively analyzes the contribution of each unit harmonic to the output torque, and presents the intrinsic connection between harmonics and output torque in detail. According to the different unit contribution ratios of harmonics to the output torque, the idea of ​​harmonic editing is determined, that is, sacrificing (reducing) the amplitude of high-order harmonics with low contribution ratios and improving (increasing) the amplitude of low-order harmonics with high contribution ratios.

[0044] 2. Based on the idea of ​​harmonic editing, the present invention adopts the inter-pole salient design, adjusts the air gap magnetic resistance, and directionally edits the amplitude of the target order harmonics, thereby deepening and developing the structural design method of magnetic field modulation, and providing an important reference for the design of different types of magnetic field modulation motors to improve the utilization rate of magnetic field harmonics.

[0045] 3. Analyze the no-load back-electromotive force amplitude and the average output torque value of the motor of the present invention, verify the results of harmonic editing, and based on the idea of ​​harmonic editing, apply the inter-pole salient pole design to a 5-phase, 10-slot, 32-pair permanent magnet pole pair, 3 winding pole pair magnetic field modulation motor, which significantly improves the motor output torque.

[0046] 4. The present invention edits the air gap harmonics of the magnetic field modulation permanent magnet motor by designing the salient poles between the rotor poles, thereby significantly improving the output torque of the magnetic field modulation permanent magnet motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 The topological structure diagram of the magnetic field modulation permanent magnet motor of the present invention is a diagram of the embodiment of the present invention that adopts the rotor inter-pole salient pole design and edits the motor magnetic field harmonics;

[0049] Figure 2 is a topological structure diagram of a conventional magnetic field modulation permanent magnet motor of conventional design adopted in an embodiment of the present invention;

[0050] Figure 3 It is an analytical model of the magnetomotive force corresponding to the permanent magnet of a unit module of the rotor in an embodiment of the present invention;

[0051] Figure 4 It is a magnetic flux path and magnetic permeance model diagram of the stator modulation tooth in a unit module according to an embodiment of the present invention;

[0052] Figure 5 is a waveform diagram of the air gap magnetic flux density when the motor according to the embodiment of the present invention is unloaded;

[0053] Figure 6 is a histogram of the air gap magnetic flux harmonic spectrum when the motor according to the embodiment of the present invention is unloaded;

[0054] Figure 7 The embodiment of the present invention calculates the contribution of each harmonic of the air gap magnetic density to the output torque according to the motor output torque;

[0055] Figure 8 is the contribution of each unit magnetic flux density to the output torque calculated according to the contribution of each order of air gap magnetic flux density to the output torque in the embodiment of the present invention;

[0056] Fig. 9 This is a model in which different rotor structures are used in the embodiments of the present invention. Fig. 9(a) is the rotor structure diagram using traditional surface-mounted permanent magnets. Fig. 9 (b) is a diagram showing the rotor structure of the motor of the present invention adopting an inter-pole salient pole design;

[0057] Fig.10 It is an analytical model of the air gap magnetic field of the motor model using the rotor inter-pole salient pole design in the embodiment of the present invention;

[0058] Fig.11 is a comparison of the air gap flux density harmonics of the motor of the embodiment of the present invention and the motor of the conventional design;

[0059] Fig.12 The comparison of the output torque of each harmonic of the air gap flux density of the motor of the embodiment of the present invention and the motor of the conventional design;

[0060] Fig.13 is a comparison of the no-load back electromotive force fundamental amplitude of the motor of the embodiment of the present invention and the motor of the conventional design;

[0061] Fig.14 It is a comparison between the average output torque and torque ripple of the motor of the embodiment of the present invention and the motor of traditional design.

[0062] In the figure: 1. stator laminated core; 2. rotor laminated core; 3. permanent magnet; 4. rotor interpole salient pole; 5. modulation pole; 6. fault-tolerant teeth; 7. armature teeth; 8. armature winding. DETAILED DESCRIPTION

[0063] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0064] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not represent any order, quantity or importance, but are only used to distinguish different components. "Including" or "comprising" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connecting" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0065] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 , Fig.11 , Fig.12 , Fig.13 , Fig.14 As shown, a method for editing the air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles comprises the following steps:

[0066] Step S1, analyzing the intrinsic relationship between torque and magnetic field harmonics according to the analytical expression of motor output torque, and locating air gap magnetic field harmonics as the key to analyzing the method of improving torque;

[0067] In step S1, refer to Figure 2 ,by Figure 2 Based on the traditional motor model, the analytical expression of the motor output torque is derived. According to the torque generation mechanism, without considering the magnetic field saturation, the analytical expression of the theoretical average output torque is as follows:

[0068]

[0069] Where, m represents the number of motor phases, I n Represents the input current amplitude, E A Represents the no-load back EMF amplitude, n s is the number of turns per phase of the motor winding, l stk Represents the axial length of the motor, N a represents the number of modulation poles on the armature teeth, t sp represents the modulation tooth arc, w s Represents the modulated inter-tooth arc, R s Represents the motor air gap radius, w o Represents the arc of the notch, P r is the number of permanent magnet poles of the motor, Z f is the number of motor modulation teeth, ω r is the rotor angular velocity of the motor, B represents the air gap flux density of the motor, and nj is defined as follows:

[0070]

[0071] From the above analytical formula of output torque, it can be found that the air gap magnetic flux B of the motor is the key parameter affecting the output torque. Therefore, to analyze the output torque, it is necessary to first analyze the air gap magnetic field of the motor and analyze the influence of the harmonic content of the air gap magnetic flux and the harmonic amplitude on the output torque.

[0072] Step S2, according to the analytical formula of air gap magnetic flux density, determine two key parameters affecting magnetic flux density: permanent magnet magnetomotive force and air gap magnetic permeability;

[0073] In step S2, the analytical formula of the air gap flux density is as follows:

[0074] B(θ s ,t)=F(θ s ,t)×Λ(θ s )

[0075] Among them, F is the permanent magnet magnetomotive force, Λ is the air gap magnetic permeance. From the analytical formula of the air gap magnetic density, it can be found that to analyze the air gap magnetic density, it is necessary to first analyze the magnetomotive force function of the rotor permanent magnet and the stator air gap magnetic permeability function of the motor.

[0076] Step S3, ignoring the magnetic field generated by the armature winding on the stator and the tooth slot structure on the stator, only considering the magnetic flux path formed by the permanent magnetic field generated by the permanent magnet on the rotor, so as to select the basic unit of the rotor structure according to the symmetry and periodicity of the rotor magnetic circuit, and establish the analytical formula of the permanent magnet magnetomotive force;

[0077] In step S3, refer to Figure 3 , Figure 3 It is the analytical model of the magnetomotive force corresponding to the permanent magnet of a unit module of the rotor, and the analytical formula of the permanent magnet magnetomotive force is obtained based on the analytical model as follows:

[0078]

[0079] Among them, F i is the harmonic amplitude of the i-th order magnetomotive force, α p is the permanent magnet pole arc coefficient, F m It can be expressed as:

[0080]

[0081] Among them, B r is the remanence of the permanent magnet, μ0 is the vacuum permeability, μ r is the relative magnetic permeability of the permanent magnet, h m is the thickness of the permanent magnet.

[0082] Step S4, simulating the magnetic flux path of the permanent magnet of the motor under the influence of the complex stator structure, establishing a fine mathematical model of the air gap permeance of the high-order harmonics, selecting the basic unit of the tooth slot structure on the stator, and establishing an analytical formula of the air gap permeance according to the mathematical model of the air gap permeance;

[0083] In step S4, refer to Figure 4 , Figure 4 It is the magnetic flux path and permeance model diagram of the stator modulation tooth in a unit module. According to the analytical model, the analytical formula of the air gap permeance can be expressed as:

[0084]

[0085] Where Λ0 is the DC component of the air gap permeability, Λ i is the i-th air gap permeability harmonic amplitude, Λ0 and Λ i It can be expressed as:

[0086]

[0087] Step S5, the calculation expression of the air gap magnetic density is programmed through MATLAB to obtain the waveform of the air gap magnetic density, such as Figure 5 As shown in Figure 2, the waveform of the air gap flux density is decomposed by Fourier, and the harmonic content diagram of the motor air gap flux density is obtained, as shown in Figure 2. Figure 6 As shown, the contribution of each harmonic in the air gap magnetic field to the output torque is studied, and the contribution ratio of each harmonic per unit to the output torque is analyzed;

[0088] In step S5, the following sub-steps are also included:

[0089] Step S5.1, selecting working harmonics from the harmonic content diagram of the motor air gap magnetic flux density, the working harmonics include low-order harmonics of 2nd, 3rd, 9th, 11th, and high-order harmonics of 32nd;

[0090] Step S5.2, see Figure 7 , Figure 7 The contribution of each harmonic of the air gap flux density to the output torque is calculated based on the analytical expression of the motor output torque, and the contribution of each harmonic order to the output torque is obtained. From the contribution of each harmonic order (such as Figure 7 As shown in the figure, it can be obtained that the contribution of the low-order 2nd and 3rd harmonics to the output torque is greater than the contribution of the high-order 32nd harmonic to the output torque.

[0091] Step S6, based on the contribution ratio of each harmonic per unit to the output torque, determine a harmonic editing strategy of reducing the amplitude of high-order harmonics with low contribution ratios and increasing the amplitude of low-order harmonics with high contribution ratios;

[0092] In step S6, refer to Figure 8 , Figure 8 The contribution of each harmonic per unit to the output torque is calculated based on the contribution of each order of air gap magnetic density to the output torque, that is, the contribution ratio of each harmonic is calculated. From the contribution ratio of each harmonic, it can be concluded that the contribution ratio of the 2nd and 3rd harmonics is greater than that of other harmonics. Therefore, the present invention determines that an innovative structural design can be adopted to improve the output torque of the motor by reducing the amplitude of high-order harmonics with low contribution ratio and increasing the amplitude of low-order harmonics with high contribution ratio.

[0093] Step S7, the goal of harmonic editing is achieved by designing salient poles between rotor poles, the amplitude of high-order harmonics with low contribution ratio is reduced, and the amplitude of low-order harmonics with high contribution ratio is increased, so that both no-load back electromotive force and output torque are improved.

[0094] In step S7, the following sub-steps are also included:

[0095] Step S7.1, based on the contribution ratio of each unit harmonic to the torque, the idea of ​​harmonic editing is to reduce the amplitude of high-order harmonics with low contribution ratio and increase the amplitude of low-order harmonics with high contribution ratio; the present invention adopts the method of designing salient poles between the rotor permanent magnets to edit each magnetic field harmonic. The specific structure is as follows Fig. 9 As shown, Fig. 9 (a) is a rotor structure with traditional design. Fig. 9 (b) is a rotor structure of the present invention adopting an inter-pole salient pole design.

[0096] Step S7.2, see Fig.10 , Fig.10 It is an air gap magnetic field analytical model of the motor model using rotor inter-pole salient pole design. Fig.10 and Figure 4 It can be clearly found that the present invention adopts the inter-pole salient pole design, which is a structural feature of editing the magnetic field harmonics by introducing the rotor;

[0097] Step S7.3, see Fig.11 , Fig.11 The comparison of the air gap magnetic flux harmonics between the motor with salient poles designed between the rotor poles and the motor with traditional design is shown in Figure 2. Fig.11 It can be clearly seen that the editing effect of the present invention on the magnetic field harmonics by designing salient poles between the rotor poles. Compared with the motor of the traditional design, the amplitude of the 2nd and 3rd harmonics in the air gap magnetic field of the motor of the present invention has been significantly improved, and the 32nd harmonic has been significantly reduced;

[0098] Step S7.4, see Fig.11 , Fig.12 It is a comparison of the contribution of each harmonic of the air gap magnetic density to the output torque of the motor using the salient poles designed between the rotor poles of the present invention and the motor using the traditional design. From the figure, it can be seen that the present invention edits the magnetic field harmonics by designing salient poles between the rotor poles, improves the low-order 2nd and 3rd harmonics that have a high contribution to the output torque, and reduces the amplitude of the high-order 32nd harmonic that has a low contribution to the output torque;

[0099] Step S7.5, see Fig.13 , Fig.13The figure shows the comparison of the no-load back electromotive force fundamental amplitude of the motor with salient poles between the rotor poles and the motor with traditional design. It can be seen from the figure that the no-load back electromotive force of the motor can be improved by using the method of editing the magnetic field harmonics by using the rotor pole salient pole design. The comparison shows that the no-load back electromotive force of the motor of the present invention is improved by 23% compared with the motor with traditional design. Fig.14 , Fig.14 The comparison of the average output torque and torque pulsation of the motor with salient poles between the rotor poles of the present invention and the motor with traditional design shows that when the input current amplitude is 4A, the torque of the motor of the present invention is increased from 17.7Nm of the traditional design to 21.9Nm, and the torque pulsation is maintained at a low level. The above results show the feasibility of the design method of the present invention to improve the output torque of the permanent magnet motor by editing the air gap harmonics of the magnetic field modulation through the rotor pole salient pole design.

[0100] In summary, the present invention discloses a design method for improving the output torque by editing the air gap harmonics of a magnetic field modulated permanent magnet motor through the rotor inter-pole salient design. According to the analytical expression of the output torque of the magnetic field modulated permanent magnet motor, the intrinsic relationship between the torque and the magnetic field harmonics is analyzed; by analyzing the total contribution of each harmonic to the output torque, the unit contribution ratio of each harmonic to the torque is analyzed; according to the different unit contribution ratios of the harmonics to the output torque, the idea of ​​harmonic editing is determined, that is, sacrificing the amplitude of the harmonic with a low contribution ratio to improve the amplitude of the harmonic with a high contribution ratio; according to the idea of ​​harmonic editing, the rotor inter-pole salient design is adopted, the air gap magnetic resistance is adjusted, and the target magnetic field harmonic amplitude is directionally edited; finally, the no-load back electromotive force amplitude and the average output torque value of the motor of the present invention are analyzed to verify the result of harmonic editing. The present invention significantly improves the output torque of the magnetic field modulated permanent magnet motor by editing the air gap harmonics of the magnetic field modulated permanent magnet motor through the rotor inter-pole salient design.

[0101] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0102] The embodiments of the present invention are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles, characterized in that: The following steps are involved: Step S1, analyzing the intrinsic relationship between torque and magnetic field harmonics according to the analytical expression of motor output torque, and locating air gap magnetic field harmonics as the key to analyzing the method of improving torque; Step S2, according to the analytical formula of air gap magnetic flux density, determine two key parameters affecting magnetic flux density: permanent magnet magnetomotive force and air gap magnetic permeability; Step S3, ignoring the magnetic field generated by the armature winding on the stator and the tooth slot structure on the stator, only considering the magnetic flux path formed by the permanent magnetic field generated by the permanent magnet on the rotor, so as to select the basic unit of the rotor structure according to the symmetry and periodicity of the rotor magnetic circuit, and establish the analytical formula of the permanent magnet magnetomotive force; Step S4, simulating the magnetic flux path of the permanent magnet of the motor under the influence of the stator structure, establishing a fine mathematical model of the air gap permeance of the high-order harmonics, selecting the basic unit of the tooth slot structure on the stator, and establishing an analytical formula of the air gap permeance according to the mathematical model of the air gap permeance; Step S5, programming the calculation expression of the air gap magnetic density through MATLAB to obtain the waveform diagram of the air gap magnetic density, perform Fourier decomposition on the waveform of the air gap magnetic density, obtain the harmonic content diagram of the motor air gap magnetic density, study the contribution of each harmonic in the air gap magnetic field to the output torque, and analyze the contribution ratio of each harmonic per unit to the output torque; Step S6, based on the contribution ratio of each harmonic per unit to the output torque, determine a harmonic editing strategy of reducing the amplitude of high-order harmonics with low contribution ratios and increasing the amplitude of low-order harmonics with high contribution ratios; Step S7, the goal of harmonic editing is achieved by designing salient poles between rotor poles, the amplitude of high-order harmonics with low contribution ratio is reduced, and the amplitude of low-order harmonics with high contribution ratio is increased, so that both no-load back electromotive force and output torque are improved.

2. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 1, characterized in that: In step S1, without considering magnetic field saturation, the analytical expression of the theoretical average output torque is as follows: Where, m represents the number of motor phases, I n Represents the input current amplitude, E A Represents the no-load back EMF amplitude, n s is the number of turns per phase of the motor winding, l stk Represents the axial length of the motor, N a represents the number of modulation poles on the armature teeth, t sp represents the modulation tooth arc, w s Represents the modulated inter-tooth arc, R s Represents the motor air gap radius, w o Represents the arc of the notch, P r is the number of permanent magnet poles of the motor, Z f is the number of motor modulation teeth, ω r is the rotor angular velocity of the motor, B represents the air gap flux density of the motor, and nj is defined as follows: From the above analytical formula of output torque, it can be found that the air gap magnetic flux B of the motor is the key parameter affecting the output torque. Therefore, to analyze the output torque, it is necessary to first analyze the air gap magnetic field of the motor and analyze the influence of the harmonic content of the air gap magnetic flux and the harmonic amplitude on the output torque.

3. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 2, characterized in that: In step S2, the analytical formula of the air gap flux density is as follows: B(θ s ,t)=F(θ s ,t)×Λ(θ s ) Among them, F is the permanent magnet magnetomotive force, Λ is the air gap magnetic permeance. From the analytical formula of the air gap magnetic density, it can be found that to analyze the air gap magnetic density, it is necessary to first analyze the magnetomotive force function of the rotor permanent magnet and the stator air gap magnetic permeability function of the motor.

4. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 3, characterized in that: In step S3, an analytical model of the magnetomotive force corresponding to the permanent magnet of a unit module of the rotor is established, and the analytical formula of the permanent magnet magnetomotive force is obtained according to the analytical model as follows: Among them, F i is the harmonic amplitude of the i-th order magnetomotive force, α p is the permanent magnet pole arc coefficient, F m It can be expressed as: Among them, B r is the remanence of the permanent magnet, μ0 is the vacuum permeability, μ r is the relative magnetic permeability of the permanent magnet, h m is the thickness of the permanent magnet.

5. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 4, characterized in that: In step S4, the stator modulates the magnetic flux path and the permeance model diagram in a unit module. According to the analytical model, the analytical formula of the air gap permeance can be expressed as: Where Λ0 is the DC component of the air gap permeability, Λ i is the i-th air gap permeability harmonic amplitude, Λ0 and Λ i It can be expressed as:

6. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 5, characterized in that: In step S5, the following sub-steps are also included: Step S5.1, selecting working harmonics from the harmonic content diagram of the motor air gap magnetic flux density, the working harmonics include low-order harmonics of 2nd, 3rd, 9th, 11th, and high-order harmonics of 32nd; Step S5.2, calculate the contribution of each harmonic of the air gap magnetic density to the output torque based on the analytical expression of the motor output torque, and obtain the contribution of each harmonic order to the output torque. From the contribution of each harmonic order, it can be obtained that the contribution of the low-order 2nd and 3rd harmonics to the output torque is greater than the contribution of the high-order 32nd harmonic to the output torque.

7. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 6, characterized in that: In step S6, based on the contribution of each order of air gap magnetic density to the output torque, the contribution of each unit harmonic to the output torque is calculated, that is, the contribution ratio of each harmonic is calculated. From the contribution ratio of each harmonic, it can be concluded that the contribution ratio of the 2nd and 3rd harmonics is greater than that of other harmonics. Therefore, the output torque of the motor can be improved by reducing the amplitude of high-order harmonics with low contribution ratio and increasing the amplitude of low-order harmonics with high contribution ratio.

8. The method for editing air gap harmonics of a magnetic field modulation permanent magnet motor by designing rotor inter-pole salient poles according to claim 7, characterized in that: In step S7, the following sub-steps are also included: Step S7.1, based on the contribution ratio of each unit harmonic to the torque, the harmonic editing idea is to reduce the amplitude of high-order harmonics with low contribution ratio and increase the amplitude of low-order harmonics with high contribution ratio; Step S7.2, analyzing the air gap magnetic field analytical model of the motor model using the rotor inter-pole salient pole design, it can be found that the inter-pole salient pole design is adopted by introducing the structural characteristics of the rotor editing magnetic field harmonics; Step S7.3, comparing the air gap magnetic flux harmonics of the motor with the rotor inter-pole salient pole design and the motor with the traditional design, it can be found that the amplitudes of the second and third harmonics in the air gap magnetic field of the motor with the rotor inter-pole salient pole design are improved, while the amplitude of the 32nd harmonic is reduced; Step S7.4, comparing the contribution of each harmonic of the air gap magnetic flux density to the output torque of the motor using the salient pole design between the rotor poles and the motor using the traditional design, it can be found that the magnetic field harmonics are edited by using the method of designing the salient pole between the rotor poles, thereby improving the low-order 2nd and 3rd harmonics that have a high contribution to the output torque and reducing the amplitude of the high-order 32nd harmonic that has a low contribution to the output torque; Step S7.5, by comparing the no-load back electromotive force fundamental amplitude of a motor with salient poles designed between rotor poles and a motor with traditional design, it can be obtained that the no-load back electromotive force of the motor can be improved by adopting the method of editing the magnetic field harmonics by adopting the salient pole design between rotor poles, and by comparing the average output torque and torque pulsation of the motor with salient poles designed between rotor poles and a motor with traditional design, it can be obtained that the average output torque of the motor can be improved by adopting the method of editing the magnetic field harmonics by adopting the salient pole design between rotor poles.

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