Multi-air-gap permanent magnet special motor air gap flux density optimization method and application

Abstract

The invention provides a multi-air-gap permanent magnet special motor air gap flux density optimization method and application. The method comprises the following steps: S1, structure pretreatment: designing a stator of a surface-mounted permanent magnet synchronous motor into a cylindrical iron core with a certain thickness; s2, target air gap flux density preliminary modeling: selecting a target air gap to be modeled, and performing preliminary modeling; and S3, introducing a coupling interference term to carry out supplementary modeling: when modeling is carried out on the selected target air gap flux density, introducing specific harmonic frequencies of other air gap flux densities to carry out supplementary modeling on the selected target air gap flux density. Mutual influence among multiple air gaps is fully considered, and specific harmonic frequencies of other air gap flux densities are innovatively introduced to carry out modeling supplement on the flux density of a certain air gap, so that the problem of flux density waveform distortion of the multi-air-gap motor is successfully solved.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic modeling technology for electric motors, specifically relating to a method and application for optimizing the air gap magnetic flux density of a multi-air gap permanent magnet special motor. Background Technology

[0002] Existing air gap modeling theories for permanent magnet motors only consider single-air gap motors and do not account for multi-air gap motors. When modeling multi-air gap motors, such as three-layer air gap motors, existing theories do not account for magnetic coupling. Specifically, magnetic lines of force pass through the outer air gap into the outer stator, then exit the outer stator through the outer and middle air gaps into the inner rotor, and finally through the inner air gap into the inner stator. This reflects the coupling situation of the three air gaps, and existing modeling theories do not extend or supplement this understanding. Summary of the Invention

[0003] The main objective of this invention is to provide a method for optimizing the air gap magnetic flux density of multi-air gap permanent magnet special motors, addressing the problems mentioned above.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for optimizing the air gap magnetic flux density of a multi-air gap permanent magnet special motor includes the following steps: S1. Structural pretreatment: The stator of the surface-mounted permanent magnet synchronous motor is designed as a cylindrical iron core of a certain thickness; S2. Preliminary modeling of the target air gap magnetic flux density: Select the target air gap to be modeled and perform preliminary modeling; S3. Introduce coupling interference terms for supplementary modeling: When modeling the selected target air gap magnetic flux density, introduce the harmonic frequencies unique to the other air gap magnetic flux densities to supplement the modeling of the selected target air gap magnetic flux density.

[0005] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: in step S1, the thickness of the cylindrical iron core is not less than twice the thickness of the permanent magnet.

[0006] As a preferred technical solution of the present invention, the specific process of preliminary modeling in step S2 is as follows: S21. Simplification of Motor Structure and Prerequisite Assumptions: To simplify the calculation process, the following assumptions need to be made regarding the motor structure and magnetic properties: the permanent magnet has uniform and isotropic magnetic properties; magnetic circuit saturation, hysteresis loss, and eddy current loss are ignored; the demagnetization characteristics of the permanent magnet are set to linear; and the windings in the armature slots are uniformly distributed. S22. Calculation of magnetomotive force of permanent magnet: The permanent magnet is equivalent to a constant magnetomotive force source. The distribution of magnetomotive force of permanent magnet is simulated by a positive and negative symmetrical trapezoidal wave function, so as to determine the specific value and variation law of magnetomotive force of permanent magnet. S23. Calculation of air gap permeability: The calculation of air gap permeability needs to take into account many factors, including the slotting effect caused by stator slotting and the pole arc effect of the motor itself. At the same time, considering the structural characteristics of the motor with double-sided slotting, a series merging calculation method is required to accurately obtain the actual value of air gap permeability. S24. Calculation of air gap magnetic flux density distribution: Based on the permanent magnet magnetomotive force obtained in step S22 and the air gap magnetic permeability calculated in step S23, the magnetic flux density distribution at different air gap locations is finally determined through the correlation calculation of magnetomotive force and magnetic permeability.

[0007] As a preferred technical solution of the present invention: when modeling the air gap magnetic flux density of a double-layer air gap permanent magnet special motor, the fundamental and quadratic terms of the magnetic flux density of the inner air gap are determined, and the fundamental and quadratic terms of the inner air gap magnetic flux density are added to the magnetic flux density modeling equation for supplementary modeling.

[0008] As a preferred technical solution of the present invention: when modeling the air gap magnetic flux density of a three-layer air gap permanent magnet special motor, the modeling is supplemented by the magnetic flux density fundamental wave coupling interference term of the outer air gap and the middle air gap, the frequency of which is determined by the pole slot matching of the permanent magnet of the motor rotor and the stator armature winding and the magnetic field line path across the air gap.

[0009] This invention also provides the application of the air gap magnetic flux density optimization method for multi-gap permanent magnet special motors as described above in the optimization of multi-port composite flux modulation motors.

[0010] This invention provides a method and application for optimizing the air gap magnetic flux density of multi-air gap permanent magnet special motors, which has the following beneficial effects: It breaks through the limitation of traditional methods being only applicable to single-air gap motors, significantly broadening the applicability of air gap magnetic flux density modeling in the motor field, and meeting the modeling needs of multi-air gap motors. By fully considering the mutual influence between multiple air gaps, it innovatively introduces the unique harmonic frequencies of the magnetic flux density of other air gaps to supplement the modeling of a certain air gap magnetic flux density, successfully solving the problem of magnetic flux density waveform distortion in multi-air gap motors. Attached Figure Description

[0011] Figure 1 The flowchart shows the air gap magnetic flux density optimization method for multi-air gap permanent magnet special motors provided by the present invention.

[0012] Figure 2 This is a diagram of an 11-pole constant magnetic permeability model.

[0013] Figure 3 The waveform of the air gap magnetic flux density obtained from finite element simulation is shown.

[0014] Figure 4This is a diagram of a double-air-gap non-constant magnetic permeability model.

[0015] Figure 5 The waveform of the external air gap magnetic flux density is shown in the double-air gap non-constant magnetic permeability model.

[0016] Figure 6a This is a Fourier decomposition diagram of the air gap magnetic flux density of the dual-air gap model.

[0017] Figure 6b This is a Fourier decomposition diagram of the air gap magnetic flux density of a single-air gap constant permeability model.

[0018] Figure 7a The waveform of the air gap magnetic flux density in the dual-air gap model is shown.

[0019] Figure 7b The waveform of the air gap magnetic flux density is shown for a single-air gap constant permeability model.

[0020] Figure 8 A three-dimensional diagram of the topology of a multi-port composite flux modulation motor.

[0021] Figure 9 The curve represents the modeling result of the method of this invention.

[0022] Figure 10 Model the result curves for existing methods. Detailed Implementation

[0023] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, taking a dual-air-gap permanent magnet special motor as an example, when modeling the air gap magnetic flux density of a dual-air-gap permanent magnet special motor, the fundamental and quadratic terms of the magnetic flux density of the inner air gap are identified, and the fundamental and quadratic terms of the inner air gap magnetic flux density are added to the magnetic flux density modeling equation for supplementation. A method for optimizing the air gap magnetic flux density of a multi-air-gap permanent magnet special motor includes the following steps: S1. Structural pretreatment: The stator of the surface-mounted permanent magnet synchronous motor is designed as a cylindrical iron core of a certain thickness to eliminate the influence of stator slotting on air gap magnetic permeability. The thickness of the cylindrical iron core shall not be less than twice the thickness of the permanent magnet.

[0025] S2. Preliminary Modeling of Target Air Gap Magnetic Flux: Select the target air gap to be modeled, and perform preliminary modeling based on the traditional air gap magnetic flux density formula: S21. Simplification of Motor Structure and Prerequisite Assumptions: To simplify the calculation process, the following assumptions need to be made regarding the motor structure and magnetic properties: the permanent magnet has uniform and isotropic magnetic properties; magnetic circuit saturation, hysteresis loss, and eddy current loss are ignored; the demagnetization characteristics of the permanent magnet are set to linear; and the windings in the armature slots are uniformly distributed. S22. Calculation of magnetomotive force of permanent magnet: The permanent magnet is equivalent to a constant magnetomotive force source. The distribution of magnetomotive force of permanent magnet is simulated by a positive and negative symmetrical trapezoidal wave function, so as to determine the specific value and variation law of magnetomotive force of permanent magnet. S23. Calculation of air gap permeability: The calculation of air gap permeability needs to take into account many factors, including the slotting effect caused by stator slotting and the pole arc effect of the motor itself. At the same time, considering the structural characteristics of the motor with double-sided slotting, a series merging calculation method is required to accurately obtain the actual value of air gap permeability. S24. Calculation of air gap magnetic flux density distribution: Based on the permanent magnet magnetomotive force obtained in step S22 and the air gap magnetic permeability calculated in step S23, the magnetic flux density distribution at different air gap locations is finally determined through the correlation calculation of magnetomotive force and magnetic permeability. ; In the formula, This represents the DC constant component of the air gap permeability function; The first of the air gap permeability functions i Second harmonic amplitude; This represents the number of tuning units; To represent spatial position angle; The mechanical rotational speed of the permanent magnet external rotor; The time it takes for the rotor to rotate; The number of pole pairs of a permanent magnet; The h-th order magnetomotive force coefficient; h The order of the Fourier decomposition of the magnetomotive force; i Let be the Fourier decomposition order of the magnetic permeability function.

[0026] S3. Introduce coupling interference terms for supplementary modeling: identify the characteristic harmonics of the remaining air gaps and supplement the target air gap model.

[0027] When modeling a certain air gap magnetic flux density, the harmonic frequencies unique to the magnetic flux density of other air gaps are introduced to supplement the modeling of that air gap magnetic flux density; when modeling the air gap magnetic flux density of a dual-air gap permanent magnet special motor, the fundamental and quadratic terms of the magnetic flux density of the inner air gap are identified, and the fundamental and quadratic terms of the inner air gap magnetic flux density are added to the magnetic flux density modeling equation to supplement it; the frequency that causes waveform distortion is caused by the fundamental frequency of the magnetic flux density of other air gaps, and its amplitude also matches the amplitude of the fundamental frequency of the magnetic permeability of other air gaps.

[0028] To study the general laws governing multi-air-gap magnetic flux coupling, it is necessary to eliminate other interfering factors. Based on the structure of traditional surface-mounted permanent magnet synchronous motors, the stator is designed as a cylindrical iron core with sufficient thickness to eliminate the influence of stator slots on air-gap permeability, thereby ensuring that the air-gap permeability remains constant. Figure 2As shown, the air gap magnetic permeability of the outer stator remains unchanged due to the absence of a toothed structure. Therefore, its air gap magnetic flux density waveform is consistent with that of the permanent magnet magnetomotive force waveform, differing only in amplitude, while the trends are essentially the same.

[0029] Figure 3 The air gap magnetic flux density waveform obtained from finite element simulation is shown, which is consistent with the magnetomotive force waveform change of the surface-mounted permanent magnet analyzed earlier. The cogging structure of a traditional permanent magnet synchronous motor has little impact on the air gap magnetic flux density, so its air gap magnetic flux density waveform can be considered consistent with the above waveform. However, the cogging structure of a field-modulated motor has a greater impact on the air gap permeability, and its air gap magnetic flux density will have two additional modulation waves compared to that of a traditional permanent magnet synchronous motor, which has been described in detail earlier.

[0030] When an air gap is added inside the permanent magnet, the model becomes a constant permeability model with both inner and outer air gaps. In this case, the air gap magnetic flux density of both the inner and outer air gaps is consistent with the magnetomotive force waveform of the permanent magnet. Changing the inner stator structure makes the inner air gap permeability no longer constant; the relevant model is as follows... Figure 4 As shown in the figure. At this point, the external air gap magnetic flux density is analyzed. Since the internal air gap is no longer a constant permeability model, but a salient pole model with a toothed structure, the external air gap magnetic flux density differs from that of a traditional permanent magnet synchronous motor. The simulation results are as follows. Figure 5 As shown. Comparison Figure 4 and Figure 5 It can be seen that in the dual-air-gap model, the external air-gap magnetic density introduces air-gap harmonics of other frequencies due to the salient pole effect of the inner stator.

[0031] right Figure 3 and Figure 5 Perform Fourier analysis, observe its harmonic composition, and plot the graph as follows: Figure 6a and Figure 6b As shown, Figure 6a This represents the air gap magnetic flux density of the double air gap model. Figure 6b This represents the air gap magnetic flux density of a single-air gap constant permeability model. In the air gap magnetic flux density waveform diagram, as shown... Figure 7a and Figure 7b As shown, Figure 7a This is a waveform diagram of the air gap magnetic flux density in a dual-air gap model. Figure 7bThe waveform of the air gap magnetic flux density in the single-gap constant permeability model shows a decrease in the magnetic flux density waveform of the 11-pole pair, while the waveforms of odd-order harmonics such as the 33rd, 55th, and 77th harmonics do not change significantly. Fourier spectrum analysis reveals that the newly added harmonic components are mainly the 2nd, 15th, and 24th harmonics. Although other harmonics exist in the figure, they are not considered in this analysis due to their small amplitude. To simplify the analysis, this embodiment only focuses on harmonics with amplitudes exceeding 1% of the fundamental amplitude, reducing complexity and concentrating on harmonic components that significantly affect motor performance. This embodiment analyzes the 2nd, 15th, and 24th harmonics. The 2nd harmonic has the most significant amplitude and is generated by the difference between the fundamental magnetomotive force of the permanent magnet and the fundamental permeability of the inner stator; the 24th harmonic is the sum of the two; and the 15th harmonic is formed by the difference between the fundamental magnetomotive force of the permanent magnet and the second harmonic permeability of the inner stator. These harmonic analyses are of great significance in revealing the complexity of the motor's magnetic field and its impact on performance. The study further quantitatively explored the influence of the non-constant magnetic permeability of the inner air gap on the magnetic flux density of the outer air gap. The second harmonic originates from the fundamental frequency modulation of the inner stator slot structure, and its amplitude is comparable to the fundamental frequency permeability of the inner stator after the magnetomotive force of the permanent magnet is normalized.

[0032] By comparing analytical calculations and finite element simulations, the results show that the error is smaller when the magnetic permeability amplitude is used to replace the harmonics of the outer air gap magnetic flux density, indicating that it is feasible to analyze the mechanism of the interaction between the inner and outer air gap magnetic flux density based on magnetic permeability.

[0033] Applications in multi-port composite flux modulation motors, with relevant motor topologies as follows: Figure 8 As shown.

[0034] The comparison results of air gap magnetic flux density modeling using the method provided in this invention and the existing analytical modeling method for magnetomotive force-permeability that does not consider harmonic compensation are as follows: Figure 9 and Figure 10 As shown, both are external air gap magnetic flux density waveforms of multi-port composite flux modulated motors. It can be seen that when using this method for modeling, the fit with the finite element simulation is high, while the fit with the existing method is poor. Using goodness-of-fit to evaluate the two, the approximation of the finite element simulation results by this method reaches 92.3%, while the approximation of the existing method is 78.6%, representing an improvement of 13.7%.

[0035] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for optimizing the air gap magnetic flux density of a multi-air gap permanent magnet special motor, characterized in that: It comprises the following steps: S1, structure pretreatment: the stator of the surface-mounted permanent magnet synchronous motor is designed as a cylindrical core with a certain thickness; S2, preliminary modeling of target air gap magnetic flux density: select the target air gap to be modeled and perform preliminary modeling; S3, introduce coupling interference terms for supplementary modeling: when modeling the selected target air gap magnetic flux density, introduce the harmonic frequency specific to the remaining air gap magnetic flux density to supplement the modeling of the selected target air gap magnetic flux density.

2. The method for optimizing the air-gap flux density of a multi-air-gap permanent-magnet special electric machine according to claim 1, characterized in that: In step S1, the thickness of the cylindrical core is not less than 2 times the thickness of the permanent magnet.

3. The method for optimizing the air-gap flux density of a multi-air-gap permanent-magnet special electric machine according to claim 1, characterized in that: In step S2, the specific process of preliminary modeling is as follows: S21, motor structure simplification and premise assumption: to simplify the calculation process, the following assumptions are made for the motor structure and magnetic properties: the magnetic properties of the permanent magnet are uniform and isotropic; the magnetic saturation phenomenon, hysteresis loss and eddy current loss are ignored; the demagnetization characteristic of the permanent magnet is set to be linear; the winding in the armature slot adopts uniform distribution; S22, permanent magnet magnetic motive force calculation: the permanent magnet is equivalent to a constant magnetic motive force source, and a positive and negative symmetric trapezoidal wave function is used to simulate the magnetic motive force distribution of the permanent magnet to determine the specific value and variation law of the permanent magnet magnetic motive force; S23, air gap permeance calculation: the calculation of air gap permeance needs to consider many factors, including the slotting effect caused by stator slotting, the pole arc effect of the motor itself; at the same time, for the structure characteristics of double-sided slotting of the motor, the series-parallel calculation method is used to accurately obtain the actual value of air gap permeance; S24, air gap magnetic flux density distribution calculation: based on the permanent magnet magnetic motive force obtained in step S22 and the air gap permeance calculated in step S23, the magnetic motive force and permeance are calculated to finally determine the magnetic flux density distribution at different air gap positions.

4. The method of claim 1, wherein: When modeling the air gap magnetic flux density of a double-layer air gap permanent magnet special motor, the magnetic flux density fundamental term and quadratic term of the inner air gap are determined, and the fundamental term and quadratic term of the inner air gap magnetic flux density are added to the magnetic flux density modeling equation for supplementary modeling.

5. The method for optimizing the air-gap flux density of a multi-air-gap permanent-magnet special electric machine according to claim 1, characterized in that: When modeling the air gap magnetic flux density of a three-layer air gap permanent magnet special motor, the modeling supplement includes the magnetic flux density fundamental coupling interference terms of the outer air gap and the middle air gap, and the frequency is determined by the pole-slot matching of the motor rotor permanent magnet and the stator armature winding and the air gap path of the magnetic flux line.

6. Application of the multi-air gap permanent magnet special motor air gap magnetic flux density optimization method according to any one of claims 1-5 in the optimization of a multi-port composite flux modulation motor.

Images